Question 1

In algebra, the quadratic equation x^2 + k1·x + k2 = 0 is known to have (x − 2) and (x + 3) as its linear factors. Using this information, determine the exact values of the coefficients k1 and k2.

Accepted Answer

Introduction / Context: This question checks your understanding of how the factorised form of a quadratic relates to its standard form x^2 + k1 x + k2. Once the roots or factors are known, you can simply expand their product to recover the coefficients. This technique is widely used when constructing polynomials from given roots and also when reverse engineering equations from factor information. Given Data / Assumptions: - The quadratic equation can be written as x^2 + k1 x + k2 = 0. - Linear factors of this quadratic are given as (x − 2) and (x + 3). - We need to find the constants k1 and k2 in terms of these factors. - Standard algebraic expansion rules apply. Concept / Approach: If a quadratic has factors (x − α) and (x − β), then its expanded form is x^2 − (α + β)x + αβ. In this problem the factors are (x − 2) and (x + 3). Instead of trying to match this pattern immediately, the most straightforward way is to multiply the two binomials directly and then compare the resulting coefficients with x^2 + k1 x + k2. Step-by-Step Solution: 1) Start with the factorised form: (x − 2)(x + 3). 2) Expand using the distributive property: x(x + 3) − 2(x + 3). 3) This gives x^2 + 3x − 2x − 6. 4) Combine like terms in the middle: x^2 + (3x − 2x) − 6 = x^2 + x − 6. 5) Compare with the standard form x^2 + k1 x + k2. 6) Clearly, k1 = 1 and k2 = −6. Verification / Alternative check: We can verify by substituting x = 2 and x = −3 into x^2 + x − 6. For x = 2, we get 4 + 2 − 6 = 0. For x = −3, we get 9 − 3 − 6 = 0. Both roots satisfy the quadratic, which confirms that the factorisation and coefficients are correct. Since the coefficient of x^2 is 1 and the two roots are fixed, there is no freedom to choose different values for k1 and k2. Why Other Options Are Wrong: Option B and Option C swap signs or swap places of coefficients incorrectly. Option D (k1 = 1, k2 = 6) would give the quadratic x^2 + x + 6, which does not have roots 2 and −3. Option E mixes both signs incorrectly. Only Option A matches exactly the coefficients obtained from the correct expansion of (x − 2)(x + 3). Common Pitfalls: A common mistake is incorrect expansion, such as x^2 + 5x − 6 if someone simply adds 2 and 3 without accounting for the minus sign. Another frequent issue is sign confusion when comparing with x^2 + k1 x + k2, especially when one or both roots are negative. Writing out every intermediate step clearly and checking by substitution helps avoid these simple but costly errors. Final Answer: Expanding the given factors and comparing coefficients shows that k1 = 1 and k2 = −6, so the correct choice is k1 = 1, k2 = -6.

Question 2

In algebra, the real numbers x and y satisfy x − y = 7. Using this relationship, evaluate the cubic difference (x − 15)^3 − (y − 8)^3 exactly, without expanding both cubes fully from scratch.

Accepted Answer

Introduction / Context: This question tests your ability to recognise structure in algebraic expressions rather than performing long and unnecessary expansions. It involves a known difference between two cubic expressions, but with shifted arguments x − 15 and y − 8. When such shifts are present, the key is to see whether these shifted quantities might actually be equal, which would make their difference very simple to evaluate. Given Data / Assumptions: - x and y are real numbers related by x − y = 7. - We must compute (x − 15)^3 − (y − 8)^3 exactly. - No specific numerical values of x and y are given, so the answer must be independent of the individual values and depend only on the relation between them. Concept / Approach: The expression (x − 15)^3 − (y − 8)^3 is a difference of cubes. Normally, one might use the identity A^3 − B^3 = (A − B)(A^2 + AB + B^2). However, before applying this identity, we should check whether A and B themselves might be equal. If the inner expressions are equal, then A^3 − B^3 is automatically zero, and the problem becomes trivial. Step-by-Step Solution: 1) Let A = x − 15 and B = y − 8. Then the expression is A^3 − B^3. 2) Compute A − B = (x − 15) − (y − 8) = x − y − 7. 3) Substitute the known relation x − y = 7, giving A − B = 7 − 7 = 0. 4) Hence A = B, which means x − 15 = y − 8. 5) When A = B, the expression A^3 − B^3 equals zero for any real values of A and B. 6) Therefore (x − 15)^3 − (y − 8)^3 = 0. Verification / Alternative check: Choose a simple numerical example that satisfies x − y = 7, for instance x = 10 and y = 3. Then x − 15 = −5 and y − 8 = −5, so both inner terms are equal. Their cubes are also equal: (−5)^3 = −125. The difference between these two identical cubes is −125 − (−125) = 0. This confirms that the result is zero for at least one example, and the algebraic reasoning shows that it must be zero for all pairs satisfying x − y = 7. Why Other Options Are Wrong: Option A (343), Option C (392), Option D (399), and Option E (49) are all non zero values that might appear if someone incorrectly plugged x − y directly into a cube without addressing the shifts, or tried an incomplete expansion. However, once we know that the shifted terms are equal, any non zero answer must be incorrect. Only Option B reflects the correct conclusion that the difference is zero. Common Pitfalls: A typical mistake is to expand both cubes fully, which is time consuming and prone to algebraic sign errors, especially under exam pressure. Another pitfall is to try to substitute x − y = 7 directly into the expression without first adjusting for the −15 and −8 shifts, missing the key insight that these shifts make the cubes identical. Recognising patterns and checking for equality of inner expressions can save valuable time and prevent errors. Final Answer: Because the relation x − y = 7 makes x − 15 and y − 8 equal, the two cubes are identical, so their difference is 0.

Question 3

In algebra with surds, the real variables x and y satisfy the simultaneous equations x − y − √18 = −1 and x + y − 3√2 = 1. Solve this system and then find the exact value of the expression 12·x·y·(x^2 − y^2).

Accepted Answer

Introduction / Context: This question combines solving a pair of simultaneous linear equations involving surds with evaluating a higher order algebraic expression. It is a good test of comfort with square root simplification, systems of equations, and manipulation of expressions such as x^2 − y^2. The structure is typical of aptitude and entrance examinations where multiple concepts are mixed in a single numerical problem. Given Data / Assumptions: - Two equations are given: x − y − √18 = −1 and x + y − 3√2 = 1. - We must first solve for x and y as real numbers. - Then we must evaluate 12·x·y·(x^2 − y^2). - Standard properties of surds and algebraic identities apply. Concept / Approach: The method is to rewrite each equation in a cleaner form and solve for x and y using addition and subtraction. We also simplify √18 as 3√2 to keep expressions consistent. Once x and y are found, we compute x^2 − y^2 using the identity x^2 − y^2 = (x − y)(x + y). Finally, we substitute all values into the expression 12·x·y·(x^2 − y^2) to obtain the exact answer in terms of √2. Step-by-Step Solution: 1) Simplify √18 as 3√2. The first equation becomes x − y − 3√2 = −1, so x − y = −1 + 3√2. 2) The second equation is x + y − 3√2 = 1, so x + y = 1 + 3√2. 3) Add the two new equations: (x − y) + (x + y) = (−1 + 3√2) + (1 + 3√2), so 2x = 6√2 and x = 3√2. 4) Subtract the first from the second: (x + y) − (x − y) = (1 + 3√2) − (−1 + 3√2), so 2y = 2 and y = 1. 5) Compute x^2 = (3√2)^2 = 9·2 = 18 and y^2 = 1. 6) Then x^2 − y^2 = 18 − 1 = 17. 7) Now evaluate 12·x·y·(x^2 − y^2) = 12 · (3√2) · 1 · 17 = 12 · 3 · 17 · √2 = 612√2. Verification / Alternative check: Substitute x = 3√2 and y = 1 back into the original equations. For the first equation, x − y − √18 becomes 3√2 − 1 − 3√2 = −1, which matches the right side. For the second equation, x + y − 3√2 becomes 3√2 + 1 − 3√2 = 1, again matching. This confirms that the solution pair is correct. Since all later calculations are straightforward substitutions and basic arithmetic, the final value 612√2 is reliable. Why Other Options Are Wrong: Option B (512√2) and Option E (408√2) arise from incorrect arithmetic when combining coefficients, for example by mis computing x^2 − y^2 or mis multiplying by 12. Option A (0) and Option D (1) would require either x or y or x^2 − y^2 to be zero, which is clearly not the case from the solved values. Only Option C matches the exact expression value from the correct solution of the system. Common Pitfalls: A common problem is failing to simplify √18 into 3√2, which makes later algebra messy and error prone. Some students also mix up addition and subtraction when combining equations, leading to incorrect values for x and y. Another frequent mistake is to forget that x^2 − y^2 can be computed quickly as (x − y)(x + y), which is simpler than squaring each term again. Careful handling of surds and consistent checking against the original equations helps avoid such slips. Final Answer: After solving the simultaneous equations and substituting into the expression, we obtain 12·x·y·(x^2 − y^2) = 612√2.

Question 4

In algebra, let the ratios p/q, r/s, and t/u all be equal to √5 (that is, p/q = r/s = t/u = √5). Using this common ratio, find the exact value of the expression (3p^2 + 4r^2 + 5t^2) / (3q^2 + 4s^2 + 5u^2).

Accepted Answer

Introduction / Context: This question tests your ability to work with proportional relationships and squared terms. When multiple ratios are equal to the same constant, you can express each numerator in terms of the denominator and the given constant. This leads to significant simplification in rational expressions, a technique often used in algebraic manipulation and in simplifying complex fractions in aptitude exams. Given Data / Assumptions: - We are given p/q = r/s = t/u = √5, with all denominators non zero. - We must evaluate (3p^2 + 4r^2 + 5t^2) / (3q^2 + 4s^2 + 5u^2). - The common ratio √5 can be used to write each numerator in terms of its denominator. - All variables are real numbers, and basic algebraic rules apply. Concept / Approach: From p/q = √5, we can write p = √5·q and hence p^2 = 5q^2. Similarly, r^2 = 5s^2 and t^2 = 5u^2. Substituting these into the numerator transforms it into a multiple of the denominator. The resulting simplification reveals that the whole fraction is just a constant, independent of the particular values of p, q, r, s, t, and u, as long as the ratio condition holds. Step-by-Step Solution: 1) Use p/q = √5 to get p = √5·q, so p^2 = (√5)^2·q^2 = 5q^2. 2) Similarly, r/s = √5 gives r^2 = 5s^2, and t/u = √5 gives t^2 = 5u^2. 3) Substitute into the numerator: 3p^2 + 4r^2 + 5t^2 = 3·5q^2 + 4·5s^2 + 5·5u^2. 4) This simplifies to 15q^2 + 20s^2 + 25u^2. 5) Factor out 5: 15q^2 + 20s^2 + 25u^2 = 5(3q^2 + 4s^2 + 5u^2). 6) The denominator is precisely 3q^2 + 4s^2 + 5u^2. 7) Therefore, the fraction is (5(3q^2 + 4s^2 + 5u^2)) / (3q^2 + 4s^2 + 5u^2) = 5. Verification / Alternative check: Choose simple numbers that satisfy the ratio condition to verify. For example, let q = s = u = 1 and therefore p = r = t = √5. Then p^2 = r^2 = t^2 = 5. The numerator becomes 3·5 + 4·5 + 5·5 = (3 + 4 + 5)·5 = 12·5 = 60. The denominator becomes 3·1^2 + 4·1^2 + 5·1^2 = 12. Thus the ratio is 60 / 12 = 5, which matches the algebraic result. Why Other Options Are Wrong: Option A (25) might arise if someone mistakenly squares the entire fraction instead of each term. Option C (1/5) is the reciprocal of the correct answer and comes from confusing p/q = √5 with q/p = √5. Option D (60) is the numerator from the verification example, forgetting to divide by the denominator. Option E (√5) results from using the ratio only once and not accounting for the squares. Only Option B matches the correctly simplified ratio. Common Pitfalls: Students sometimes forget that if p/q = k, then p^2/q^2 = k^2, not k. Others treat each term separately but forget to factor out 5 in the numerator, making cancellation less obvious. It is also easy to confuse p/q with q/p. Writing the expressions clearly and keeping track of squares avoids these issues and makes simplification straightforward. Final Answer: Using the common ratio p/q = r/s = t/u = √5 and simplifying the squared terms, the fraction evaluates to 5.

Question 5

In trigonometry, the angles A, B, and C have the values A = 30°, B = 60°, and C = 135°. Evaluate the expression (sin A)^3 + (cos B)^3 + (tan C)^3 − 3·sin A·cos B·tan C exactly.

Accepted Answer

Introduction / Context: This question is designed to highlight a standard algebraic identity involving the sum of cubes. By combining this identity with exact trigonometric values for special angles, the expression becomes much easier to evaluate. The problem is a good example of how algebra and trigonometry work together in aptitude style questions, and it rewards recognition of structure instead of raw computation. Given Data / Assumptions: - Angle A is 30 degrees, so sin A is a standard special value. - Angle B is 60 degrees, so cos B is also a standard special value. - Angle C is 135 degrees, so tan C is a standard value in the second quadrant. - We must compute (sin A)^3 + (cos B)^3 + (tan C)^3 − 3·sin A·cos B·tan C exactly. - All calculations use exact surd values rather than decimal approximations. Concept / Approach: Recall the identity a^3 + b^3 + c^3 − 3abc = (a + b + c)(a^2 + b^2 + c^2 − ab − bc − ca). If a + b + c equals zero, then the entire expression is zero. In this problem, we can let a = sin A, b = cos B, and c = tan C. We compute each of these exactly using known trigonometric values and then check whether their sum is zero. If it is, the original expression immediately becomes zero by the identity. Step-by-Step Solution: 1) Compute sin 30° = 1/2. 2) Compute cos 60° = 1/2. 3) Compute tan 135°. Since tan 135° = tan(180° − 45°) and tangent is negative in the second quadrant, tan 135° = −tan 45° = −1. 4) Set a = sin A = 1/2, b = cos B = 1/2, and c = tan C = −1. 5) Find a + b + c = 1/2 + 1/2 − 1 = 1 − 1 = 0. 6) Use the identity a^3 + b^3 + c^3 − 3abc = (a + b + c)(a^2 + b^2 + c^2 − ab − bc − ca). 7) Because a + b + c = 0, the entire expression equals 0, regardless of the second factor. Verification / Alternative check: We can compute the expression directly to confirm. First, a^3 = (1/2)^3 = 1/8 and b^3 = 1/8. Also c^3 = (−1)^3 = −1. Thus a^3 + b^3 + c^3 = 1/8 + 1/8 − 1 = 1/4 − 1 = −3/4. Next, the product 3abc = 3·(1/2)·(1/2)·(−1) = 3·(1/4)·(−1) = −3/4. So a^3 + b^3 + c^3 − 3abc = −3/4 − (−3/4) = 0. This matches the identity based result exactly. Why Other Options Are Wrong: Options A (1), B (8), D (9), and E (−1) are typical distractors that might result from partial calculations or ignoring the negative sign of tan 135°. For instance, forgetting that tangent is negative in the second quadrant can flip the sign of c and change the entire expression. Only Option C matches the exact value obtained using both the identity and direct computation. Common Pitfalls: The main pitfalls are using approximate decimal values instead of exact surds and overlooking the sign of tangent in different quadrants. Many students also forget or misuse the sum of cubes identity, attempting long and error prone expansions instead. Recognising the structure a^3 + b^3 + c^3 − 3abc and checking whether a + b + c vanishes is a powerful shortcut that prevents mistakes and saves time. Final Answer: Using exact special angle values and the sum of cubes identity, the given trigonometric expression simplifies to 0.

Question 6

In algebra, the non zero real numbers x, y, and z satisfy (1/x) + (1/y) + (1/z) = 0 and also x + y + z = 9. Using these conditions, find the exact value of x^3 + y^3 + z^3 − 3xyz.

Accepted Answer

Introduction / Context: This question links symmetric sums of variables with their reciprocals. It is a classic application of algebraic identities for sums of cubes and relationships between coefficients and roots. Instead of requiring explicit values of x, y, and z, the problem invites you to work symbolically with identities, which is a powerful technique in higher level algebra and many competitive exams. Given Data / Assumptions: - x, y, and z are non zero real numbers. - We are told that (1/x) + (1/y) + (1/z) = 0. - We also know that x + y + z = 9. - We must compute x^3 + y^3 + z^3 − 3xyz using these relationships. Concept / Approach: First, use the reciprocal condition to derive information about xy + yz + zx. Since (1/x) + (1/y) + (1/z) equals (xy + yz + zx) divided by xyz, the equality to zero forces the numerator xy + yz + zx to be zero (because xyz is non zero). Then, apply the identity x^3 + y^3 + z^3 − 3xyz = (x + y + z)(x^2 + y^2 + z^2 − xy − yz − zx). With x + y + z and xy + yz + zx known, we can compute x^2 + y^2 + z^2 and then the entire expression. Step-by-Step Solution: 1) Use the reciprocal condition: (1/x) + (1/y) + (1/z) = (xy + yz + zx) / (xyz) = 0. 2) Because xyz is non zero, the only way for the fraction to be zero is if xy + yz + zx = 0. 3) We also know that x + y + z = 9. 4) Compute (x + y + z)^2: this equals x^2 + y^2 + z^2 + 2(xy + yz + zx). 5) Substitute the known values: 9^2 = x^2 + y^2 + z^2 + 2·0, so x^2 + y^2 + z^2 = 81. 6) Now apply the identity x^3 + y^3 + z^3 − 3xyz = (x + y + z)(x^2 + y^2 + z^2 − xy − yz − zx). 7) Substitute the values: x + y + z = 9, x^2 + y^2 + z^2 = 81, and xy + yz + zx = 0, giving 9·(81 − 0) = 9·81 = 729. Verification / Alternative check: You can test with a simple concrete triple that satisfies the conditions. For example, take x = 3, y = 3, and z = 3. Then x + y + z = 9, but (1/x) + (1/y) + (1/z) = 1, so this choice does not satisfy the reciprocal condition. A more suitable triple is harder to guess directly, but the algebraic derivation does not require actual values. The identity used is standard and holds for any real x, y, and z, so as long as the symmetric sums satisfy the given relations, the final result 729 is valid for all such triples. Why Other Options Are Wrong: Option A (6561) would correspond to squaring 81 again or mis applying the identity. Option B (361) and Option D (81) are typical distractors from mis computing x^2 + y^2 + z^2 or forgetting to multiply by x + y + z. Option E (243) appears if you mistakenly multiply 27 by 9 or mis handle cubes. Only Option C exactly matches the result of applying the correct identity with the given sums. Common Pitfalls: Common errors include forgetting that (1/x) + (1/y) + (1/z) simplifies to (xy + yz + zx) / (xyz), or treating xy + yz + zx as zero without checking that xyz is non zero. Some students mis recall the identity for x^3 + y^3 + z^3 − 3xyz or drop terms like xy + yz + zx prematurely. Writing out identities carefully and working step by step prevents these mistakes and strengthens algebraic fluency. Final Answer: Using the symmetric sums and the standard identity for cubes, the value of x^3 + y^3 + z^3 − 3xyz is 729.

Question 7

In algebra with powers and reciprocals, suppose x is a real number greater than 1 such that x^4 + 1/x^4 = 34. Using this condition, find the exact value of the expression x^3 − 1/x^3.

Accepted Answer

Introduction / Context: This question tests manipulation of expressions involving powers of a variable and its reciprocal. Instead of solving for x directly, you can use algebraic identities that connect x^4 + 1/x^4 with x^2 + 1/x^2 and x − 1/x. These kinds of problems are frequently asked in aptitude tests because they reward a structured approach and knowledge of standard identities over blind computation. Given Data / Assumptions: - x is a real number with x greater than 1, so x and 1/x are both positive, and x − 1/x is positive. - We are given x^4 + 1/x^4 = 34. - We must determine x^3 − 1/x^3 exactly. - Only algebraic identities and logical reasoning are needed, no numerical approximation of x itself is required. Concept / Approach: First, recall that (x^2 + 1/x^2)^2 = x^4 + 2 + 1/x^4. This identity allows us to compute x^2 + 1/x^2 from the given sum of fourth powers. Next, use the identity (x − 1/x)^2 = x^2 + 1/x^2 − 2 to find x − 1/x. Finally, use the identity x^3 − 1/x^3 = (x − 1/x)(x^2 + 1 + 1/x^2) to get the desired value. The condition x greater than 1 helps us choose the correct sign when taking square roots. Step-by-Step Solution: 1) Start with the identity (x^2 + 1/x^2)^2 = x^4 + 2 + 1/x^4. 2) Substitute x^4 + 1/x^4 = 34 to get (x^2 + 1/x^2)^2 = 34 + 2 = 36. 3) Therefore x^2 + 1/x^2 = ±6. But x^2 + 1/x^2 is always positive, so x^2 + 1/x^2 = 6. 4) Use the identity (x − 1/x)^2 = x^2 + 1/x^2 − 2, which gives (x − 1/x)^2 = 6 − 2 = 4. 5) Hence x − 1/x = ±2. Since x is greater than 1, x − 1/x is positive, so x − 1/x = 2. 6) Use the identity x^3 − 1/x^3 = (x − 1/x)(x^2 + 1 + 1/x^2). 7) Substitute x − 1/x = 2 and x^2 + 1/x^2 = 6, giving x^3 − 1/x^3 = 2 · (6 + 1) = 2 · 7 = 14. Verification / Alternative check: We can check consistency by working backwards. Suppose x − 1/x = 2. Then x^2 − 2 + 1/x^2 = 4, so x^2 + 1/x^2 = 6. Squaring this gives (x^2 + 1/x^2)^2 = 36, which equals x^4 + 2 + 1/x^4, so x^4 + 1/x^4 = 34, matching the given condition. This confirms that the chain of identities is coherent and that x^3 − 1/x^3 = 14 is correct. Why Other Options Are Wrong: Option A (6) is the value of x^2 + 1/x^2, not x^3 − 1/x^3. Option C (8) and Option E (−14) arise from mis using signs or forgetting that x − 1/x must be positive when x greater than 1. Option D (0) would mean x^3 = 1/x^3, which implies x^6 = 1, not consistent with the given x^4 + 1/x^4 = 34. Only Option B matches the correctly derived value. Common Pitfalls: Learners sometimes try to solve for x directly using a high degree equation, which is unnecessary and much harder. Another common mistake is forgetting to add the middle term 2 when using the identity for x^4 + 1/x^4, or mishandling signs when taking square roots. Writing the relevant identities separately and substituting carefully step by step is the safest way to handle such expressions. Final Answer: Using identities for powers of x and its reciprocal, the value of x^3 − 1/x^3 is 14.

Question 8

In algebra, the real numbers x and y satisfy x = 1 − y and x^2 = 2 − y^2 simultaneously. Using these two equations, determine the exact value of the product x·y.

Accepted Answer

Introduction / Context: This question involves solving a system of equations that contains both linear and quadratic relationships between x and y. Once x and y are related through two equations, the task is to find the value of the product x·y without necessarily computing each variable individually in decimal form. This style of problem is common in algebra based aptitude tests, where the focus is on symbolic manipulation rather than heavy numerical computation. Given Data / Assumptions: - x and y are real numbers. - They satisfy x = 1 − y (a linear relation) and x^2 = 2 − y^2 (a quadratic relation). - We are asked to find the exact value of x·y. - Standard algebraic rules and methods for solving simultaneous equations apply. Concept / Approach: We use substitution. Since x = 1 − y, we can substitute this expression for x in the second equation x^2 = 2 − y^2. After simplification, we obtain an equation solely in terms of y, which we can then solve. Once y is known, x follows from x = 1 − y. Finally, we compute the product x·y. Because the equations are symmetric in a certain way, the product will turn out to be the same for both solution pairs, leading to a unique value for x·y. Step-by-Step Solution: 1) From x = 1 − y, substitute into x^2 = 2 − y^2 to get (1 − y)^2 = 2 − y^2. 2) Expand the left side: (1 − y)^2 = 1 − 2y + y^2. 3) Set up the equation: 1 − 2y + y^2 = 2 − y^2. 4) Bring all terms to one side: 1 − 2y + y^2 − 2 + y^2 = 0, which simplifies to 2y^2 − 2y − 1 = 0. 5) Solve the quadratic 2y^2 − 2y − 1 = 0 using the quadratic formula, giving y = (2 ± √(4 + 8)) / 4 = (2 ± √12) / 4 = (2 ± 2√3) / 4 = (1 ± √3) / 2. 6) Use x = 1 − y. For y = (1 + √3) / 2, x = (1 − √3) / 2. For y = (1 − √3) / 2, x = (1 + √3) / 2. 7) In both cases, the product x·y = ((1 + √3)/2)·((1 − √3)/2) = (1 − 3) / 4 = −2 / 4 = −1/2. Verification / Alternative check: We can substitute one pair, for example x = (1 + √3)/2 and y = (1 − √3)/2, back into the original equations. For the linear relation, x = 1 − y becomes (1 + √3)/2 = 1 − (1 − √3)/2, which simplifies correctly. For the quadratic relation, x^2 = 2 − y^2, computing each side shows equality. Since both solution pairs lead to the same product x·y, the final answer −1/2 is consistent and unique for the product. Why Other Options Are Wrong: Option B (1), Option C (−1), Option D (2), and Option E (1/2) correspond to guessing the product or confusing it with sums like x + y or differences like x − y. None of these values match the exact product obtained from the correct solution of the system. Only Option A reflects the properly computed value of x·y. Common Pitfalls: Some learners try to solve for x and y numerically too early, leading to approximate decimal values and rounding errors instead of an exact product. Others may expand (1 − y)^2 incorrectly, or forget to move all terms to one side of the quadratic equation. The symmetry between the two solutions might also be overlooked, leading to confusion about which product to choose. Working symbolically and carefully checking algebraic steps prevents these errors. Final Answer: Solving the system and multiplying the resulting values of x and y shows that x·y = −1/2.

Question 9

In trigonometric simplification, evaluate the algebraic trigonometric product: (sec A + cos A) (sec A − cos A). Express the result in its simplest form using basic trigonometric identities.

Accepted Answer

Introduction / Context: This question focuses on simplification of a trigonometric expression that looks similar to the algebraic form (a + b)(a − b) = a^2 − b^2. The goal is to rewrite the given product in terms of simpler trigonometric functions and then match it to one of the given options. Problems like this are common in trigonometry sections of aptitude tests because they test both algebraic pattern recognition and understanding of trigonometric identities. Given Data / Assumptions: - The expression to simplify is (sec A + cos A)(sec A − cos A). - All angles are within a domain where sec A and cos A are defined, and cos A is non zero (so sec A exists). - We should use known identities such as sec A = 1 / cos A and sec^2 A = 1 + tan^2 A. Concept / Approach: First observe that (sec A + cos A)(sec A − cos A) has the form (u + v)(u − v) = u^2 − v^2. Therefore, the product simplifies to sec^2 A − cos^2 A. Then we express sec^2 A as 1 / cos^2 A and perform algebraic simplification. The final result can be transformed into an equivalent expression involving sin^2 A and tan^2 A, which can then be matched with one of the answer choices. Step-by-Step Solution: 1) Recognise a difference of squares: (sec A + cos A)(sec A − cos A) = sec^2 A − cos^2 A. 2) Replace sec^2 A with 1 / cos^2 A, giving 1 / cos^2 A − cos^2 A. 3) Write this as a single fraction: (1 − cos^4 A) / cos^2 A. 4) Factor the numerator: 1 − cos^4 A = (1 − cos^2 A)(1 + cos^2 A). 5) Use 1 − cos^2 A = sin^2 A. The expression becomes sin^2 A (1 + cos^2 A) / cos^2 A. 6) Split the fraction: sin^2 A / cos^2 A + sin^2 A. 7) Recognise sin^2 A / cos^2 A as tan^2 A, so the final simplified form is tan^2 A + sin^2 A. Verification / Alternative check: Take a simple angle where both sine and cosine have known values, such as A = 45 degrees. Then sec 45° = √2 and cos 45° = √2 / 2. The original product becomes (√2 + √2/2)(√2 − √2/2). Evaluating this numerically gives a certain value. Computing sin^2 A + tan^2 A at A = 45° using sin 45° = √2/2 and tan 45° = 1 yields the same numerical result, confirming that the simplification sin^2 A + tan^2 A is correct. Why Other Options Are Wrong: Option A (2 tan^2 A) and Option B (2 sin^2 A) miscount the factors. Option C (sin^2 A * tan^2 A) multiplies the two terms instead of adding them. Option E (sec^2 A − 1) is equal to tan^2 A alone, which does not include the sin^2 A term we derived. Only Option D matches exactly the simplified expression tan^2 A + sin^2 A. Common Pitfalls: One frequent error is to stop at sec^2 A − cos^2 A and try to match it directly to the options without further simplification. Another mistake is mis applying identities, for example, writing sec^2 A as 1 + sin^2 A or confusing tan^2 A with sin^2 A / cos A. Carefully using standard identities and performing algebraic steps one at a time avoids these issues. Final Answer: The given product simplifies to sec^2 A − cos^2 A, which further reduces to sin^2 A + tan^2 A.

Question 10

In trigonometric simplification, evaluate the expression: cosec^2 A − cot^2 A + tan^2 A. Express the result in the simplest standard trigonometric form.

Accepted Answer

Introduction / Context: This problem tests your knowledge of basic trigonometric identities involving cosec, cot, tan, and sec. The expression is constructed so that standard Pythagoras identities simplify a large part of it. Such questions are common in trigonometry sections to ensure that learners are fluent in converting between different trigonometric functions and know the core relationships among them. Given Data / Assumptions: - The expression is cosec^2 A − cot^2 A + tan^2 A. - The angle A is chosen so that all functions are defined (in particular, sin A and cos A are non zero where needed). - We are to express the final result in the simplest form, using standard functions like sec^2 A if possible. Concept / Approach: There are two key identities to use. First, cosec^2 A − cot^2 A = 1, which is the Pythagoras identity for cosec and cot. Second, 1 + tan^2 A = sec^2 A. The given expression is therefore a direct combination of these two identities. Evaluate the difference in the first two terms to obtain 1, then add tan^2 A and recognise the second identity. Step-by-Step Solution: 1) Recall the identity for cosecant and cotangent: cosec^2 A − cot^2 A = 1. 2) Apply this directly to the first two terms of the expression, replacing them with 1. 3) The expression now becomes 1 + tan^2 A. 4) Recall the standard identity relating tangent and secant: sec^2 A = 1 + tan^2 A. 5) Substitute this identity to obtain the final simplified form. 6) Therefore, cosec^2 A − cot^2 A + tan^2 A = sec^2 A. Verification / Alternative check: You can check this numerically for a simple angle such as A = 45 degrees. Then sin 45° = cos 45° = √2/2, so tan 45° = 1, sec 45° = √2, cosec 45° = √2, and cot 45° = 1. Substituting, we get cosec^2 45° − cot^2 45° + tan^2 45° = (2) − (1) + (1) = 2. On the other hand, sec^2 45° = (√2)^2 = 2. Both sides match, which confirms the identity based simplification. Why Other Options Are Wrong: Option A (2 cos 2A) and Option E (1 + cos^2 A) do not follow from the standard Pythagoras identities used here. Option B (1 − sin^2 A) equals cos^2 A, which is different from sec^2 A. Option D (sec A * tan A) is a derivative related identity rather than a Pythagoras type. Only Option C exactly matches the simplified expression 1 + tan^2 A. Common Pitfalls: Some students confuse the identity for cosec and cot with that for sec and tan, writing cosec^2 A − cot^2 A as cot^2 A wrongly or mis placing the minus sign. Another common error is to stop at 1 + tan^2 A without recognising that this is identical to sec^2 A. Regular practice with the four core Pythagoras identities in trigonometry helps in remembering and applying them correctly. Final Answer: Simplifying using standard identities gives cosec^2 A − cot^2 A + tan^2 A = sec^2 A.

Question 11

In a digit counting problem, you write all the integers from 121 to 1346 inclusive on a typewriter. If each digit typed counts as one key press, how many digit key presses are required in total to type all these numbers?

Accepted Answer

Introduction / Context: This question tests your understanding of place value and counting techniques. It asks for the total number of digit key presses needed to type all numbers in a given range, which is a standard type of aptitude puzzle. Rather than writing out each number individually, you should break the interval into groups with the same number of digits and then multiply by the number of digits per number. Given Data / Assumptions: - We are typing all integers from 121 up to 1346, inclusive at both ends. - Each digit typed is one key press, and we ignore spaces, commas, or any other formatting characters. - Numbers between 121 and 999 are three digit numbers, and numbers from 1000 to 1346 are four digit numbers. Concept / Approach: The method is to split the range into two continuous sub ranges where the number of digits is constant. From 121 to 999, every number has three digits. From 1000 to 1346, every number has four digits. We count how many numbers lie in each sub range, multiply by the number of digits in each, and then add the results. This avoids dealing with each number individually and makes the calculation efficient and accurate. Step-by-Step Solution: 1) First consider the three digit numbers from 121 to 999 inclusive. 2) The count of these numbers is 999 − 121 + 1 = 879. 3) Each of these numbers has 3 digits, so the total digit presses for this part is 879 · 3 = 2637. 4) Next consider the four digit numbers from 1000 to 1346 inclusive. 5) The count of these numbers is 1346 − 1000 + 1 = 347. 6) Each has 4 digits, so the total digit presses for this part is 347 · 4 = 1388. 7) Add the two parts: 2637 + 1388 = 4025 digit key presses in total. Verification / Alternative check: We can quickly check the boundaries. From 121 to 999, we start at the first three digit number greater than or equal to 121 and go up to the last three digit number. The formula 999 − 121 + 1 is standard for inclusive ranges. Similarly, for four digit numbers, 1000 to 1346 inclusive gives 347 numbers. Multiplying and adding again gives 2637 + 1388, and the sum 4025 is consistent with both arithmetic and the structure of the number line. Why Other Options Are Wrong: Options A (4018), B (4021), and E (4035) are very close and arise from small counting mistakes, such as off by one errors at boundaries or mis multiplying 879 or 347. Option C (3675) indicates a more serious error, possibly counting only part of the range or using the wrong number of digits per group. Only Option D exactly matches the total obtained by careful grouping and arithmetic. Common Pitfalls: A common error is to forget that both endpoints are included, leading to subtracting without adding one. Another mistake is to forget that 1000 introduces the four digit range, causing all numbers to be treated as three digit numbers. Students also sometimes mis calculate products like 879 · 3, especially under time pressure. Keeping track of the digit length per range and checking simple multiplication carefully helps avoid these pitfalls. Final Answer: The total number of digit key presses required to type all integers from 121 to 1346 inclusive is 4025.

Question 12

In polynomial algebra, consider the cubic polynomial p·x^3 − q·x^2 − 7x − 6. If this polynomial is exactly divisible by x^2 − x − 6 (that is, its remainder is zero), determine the values of the constants p and q.

Accepted Answer

Introduction / Context: This question uses the idea of polynomial divisibility. If a cubic polynomial is divisible by a quadratic factor, then the roots of the quadratic must also be roots of the cubic. This allows us to set up equations involving the unknown parameters p and q by substituting the roots into the cubic and setting the resulting values to zero. This is a standard technique in algebra for determining unknown coefficients in polynomials. Given Data / Assumptions: - The cubic polynomial is p·x^3 − q·x^2 − 7x − 6. - It is divisible by x^2 − x − 6. - The quadratic factor x^2 − x − 6 can be factored further, which reveals its roots. - We need to find exact values of p and q such that the divisibility condition holds. Concept / Approach: First, factor the quadratic x^2 − x − 6 to find its roots. If x^2 − x − 6 = (x − 3)(x + 2), then the roots are x = 3 and x = −2. If the cubic is divisible by this quadratic, then x = 3 and x = −2 must also be roots of the cubic p·x^3 − q·x^2 − 7x − 6. Therefore, substituting x = 3 and x = −2 into the cubic must give zero, yielding two linear equations in p and q that can be solved simultaneously. Step-by-Step Solution: 1) Factor the quadratic: x^2 − x − 6 = (x − 3)(x + 2), so the roots are 3 and −2. 2) Let f(x) = p·x^3 − q·x^2 − 7x − 6. 3) For x = 3, divisibility implies f(3) = 0. Compute f(3) = p·3^3 − q·3^2 − 7·3 − 6 = 27p − 9q − 21 − 6. 4) Simplify: f(3) = 27p − 9q − 27. Set this equal to zero to get 27p − 9q − 27 = 0, or dividing by 9, 3p − q − 3 = 0. 5) For x = −2, we require f(−2) = 0. Compute f(−2) = p·(−8) − q·4 − 7·(−2) − 6 = −8p − 4q + 14 − 6. 6) Simplify: f(−2) = −8p − 4q + 8. Set this equal to zero: −8p − 4q + 8 = 0, or dividing by −4, 2p + q − 2 = 0. 7) Solve the system 3p − q − 3 = 0 and 2p + q − 2 = 0. Adding them gives 5p − 1 = 0, so p = 1. Then 2(1) + q − 2 = 0 gives q = 0. Verification / Alternative check: Substitute p = 1 and q = 0 back into the cubic, giving x^3 − 7x − 6. Factor the quadratic divisor x^2 − x − 6. Perform polynomial long division or factor x^3 − 7x − 6 as (x^2 − x − 6)(x + 1) to check divisibility. Multiplying (x^2 − x − 6)(x + 1) gives x^3 − 7x − 6, confirming that with p = 1 and q = 0 the cubic is indeed divisible by the quadratic with no remainder. Why Other Options Are Wrong: Other option pairs for p and q fail the divisibility test. For example, choosing p = 0 or q = 1 leads to values of f(3) or f(−2) that are non zero, meaning at least one of the quadratic roots is not a root of the cubic. Only the pair p = 1, q = 0 satisfies f(3) = 0 and f(−2) = 0 simultaneously, ensuring exact divisibility by x^2 − x − 6. Common Pitfalls: Mistakes often arise from incorrect substitution of the roots into the cubic or from arithmetic errors in simplifying coefficients. When solving the system for p and q, forgetting to divide by common factors can make the equations look more complicated than they are. It is also easy to assume divisibility from only one root and not check the other, which can lead to an incorrect conclusion. Systematic substitution and careful algebra avoid these traps. Final Answer: The only values that make the cubic polynomial p·x^3 − q·x^2 − 7x − 6 divisible by x^2 − x − 6 are p = 1, q = 0.

Question 13

In polynomial algebra, consider the cubic polynomial p·x^3 − 2x^2 − q·x + 18. If this polynomial is completely divisible by x^2 − 9 (that is, it has no remainder), find the ratio p : q.

Accepted Answer

Introduction / Context: This problem again uses polynomial divisibility, but the goal is to find a ratio between two coefficients rather than their exact individual values. The factor x^2 − 9 has simple roots, and knowing that the cubic is divisible by this quadratic means each of those roots must also be roots of the cubic. This gives us equations relating p and q, from which we can determine their ratio p : q. Given Data / Assumptions: - The cubic polynomial is p·x^3 − 2x^2 − q·x + 18. - It is divisible by x^2 − 9, which factors as (x − 3)(x + 3). - Therefore 3 and −3 are roots of the cubic polynomial. - We must determine the ratio p : q, not necessarily the individual values. Concept / Approach: Let f(x) = p·x^3 − 2x^2 − q·x + 18. Because f(x) is divisible by x^2 − 9, f(3) = 0 and f(−3) = 0. Substituting x = 3 and x = −3 into f(x) gives two equations involving p and q. Solving this system reveals a relationship between p and q. Even if the system does not pin down unique numeric values, it will give a proportional relationship, which is exactly what is asked for in the ratio p : q. Step-by-Step Solution: 1) Define f(x) = p·x^3 − 2x^2 − q·x + 18. 2) Since x^2 − 9 = (x − 3)(x + 3), the roots are x = 3 and x = −3, so f(3) = 0 and f(−3) = 0. 3) Compute f(3): f(3) = p·27 − 2·9 − q·3 + 18 = 27p − 18 − 3q + 18 = 27p − 3q. 4) Set f(3) = 0, giving 27p − 3q = 0, or dividing by 3, 9p − q = 0, so q = 9p. 5) Compute f(−3): f(−3) = p·(−27) − 2·9 − q·(−3) + 18 = −27p − 18 + 3q + 18 = −27p + 3q. 6) Set f(−3) = 0, giving −27p + 3q = 0, or dividing by 3, −9p + q = 0, which is the same relation q = 9p. 7) Thus the ratio p : q satisfies q = 9p, so p : q = 1 : 9. Verification / Alternative check: We can choose a convenient value for p and compute q accordingly. For example, let p = 1, then q = 9. The polynomial becomes x^3 − 2x^2 − 9x + 18. Factor x^2 − 9 as (x − 3)(x + 3) and check if this divides the cubic. By performing polynomial division or grouping, you can confirm that x^3 − 2x^2 − 9x + 18 factors as (x^2 − 9)(x − 2), confirming that p : q = 1 : 9 is consistent with the divisibility condition. Why Other Options Are Wrong: Options B (1 : 3), C (3 : 1), D (9 : 1), and E (2 : 9) all represent different proportional relationships that do not satisfy the equations obtained from f(3) = 0 and f(−3) = 0. If any of these ratios were used, either f(3) or f(−3) would be non zero, meaning the polynomial would not be divisible by x^2 − 9. Only Option A reflects the correct ratio p : q = 1 : 9 that satisfies both conditions. Common Pitfalls: A common error is to compute f(3) correctly but forget to use f(−3), or vice versa, which can lead to incomplete or incorrect relationships. Another mistake is mishandling signs when substituting negative values like −3 into the polynomial. Dividing both sides of the equations by common factors also helps simplify the system and makes the ratio easier to identify. Carefully writing substitutions and checking arithmetic can prevent these errors. Final Answer: From the divisibility conditions at x = 3 and x = −3, we find that q = 9p, so the required ratio is 1:9.

Question 14

In algebra with exponents, let x and y be non zero real numbers such that (x / y)^(a − 4) = (y / x)^(2a − 5) for all real values of the parameter a for which these expressions are defined. Based on this condition, what can be concluded about the rel…

Accepted Answer

Introduction / Context: This question uses properties of exponential expressions to deduce a relationship between two non zero real numbers x and y. Rather than asking you to find specific values of x or y, it asks for a qualitative relationship. The key is to interpret the equality of powers carefully and recognise how it must hold for all real values of the parameter a, which imposes strong restrictions on the base x / y. Given Data / Assumptions: - x and y are non zero real numbers. - The equality (x / y)^(a − 4) = (y / x)^(2a − 5) holds for all real values of a for which both sides are defined. - We must determine the relationship between x and y implied by this identity. - Standard rules of exponents and logarithms apply, and we consider real valued expressions. Concept / Approach: First, notice that y / x is the reciprocal of x / y. We can therefore rewrite the right hand side in terms of the same base as the left. This leads to an equation of the form (x / y)^(a − 4) = (x / y)^(something involving a). For this identity to hold for all admissible real values of a, either the exponents must match for all a, or the base x / y must be a special value such that any exponent produces the same result. Examining these possibilities reveals that the only consistent choice is x / y = 1, which implies x = y. Step-by-Step Solution: 1) Start with (x / y)^(a − 4) = (y / x)^(2a − 5). 2) Observing that y / x = (x / y)^(−1), rewrite the right side as ((x / y)^(−1))^(2a − 5) = (x / y)^(−(2a − 5)). 3) The equation becomes (x / y)^(a − 4) = (x / y)^(−(2a − 5)). 4) Let k = x / y. Then the equation is k^(a − 4) = k^(−(2a − 5)). 5) For this to hold for all real a where the expressions are defined, the only way is for the base k to be such that k^t is the same for all exponents t. This happens only when k = 1 (for real, positive bases), since 1 raised to any power equals 1. 6) Therefore, x / y = 1, which implies x = y. Verification / Alternative check: If x = y, then x / y = 1 and y / x = 1. In that case, both sides of the original equation become 1 raised to some exponent, which is always 1 whenever the exponent is defined. Hence the equality holds for all real a, confirming that x = y is sufficient. Conversely, if x and y were unequal, then x / y would not equal 1, and k^t would vary with t for real exponents, making it impossible for k^(a − 4) to equal k^(−(2a − 5)) for all choices of a. Thus x = y is also necessary. Why Other Options Are Wrong: Options A (x > y), C (x < y), and E (x ≥ y) describe partial order relationships that do not guarantee the equality for all values of a. For most unequal positive x and y, the equality could hold at best for a few specific values of a, not for all. Option B (Cannot be determined) ignores the very strong condition that the equality is valid for every admissible a, which forces a unique relationship. Only Option D correctly captures the necessary and sufficient condition x = y. Common Pitfalls: A common misunderstanding is to equate the exponents directly for all a, which leads to a condition on a instead of on x and y, or to consider only a single value of a. Another pitfall is not recognising that 1 is the only positive real base for which raising to any power gives the same result. Thinking carefully about the behaviour of exponential functions with different bases is crucial to avoid these errors. Final Answer: The only way for the equality of powers to hold for all real values of a is if x / y = 1, that is, x = y.

Question 15

In algebra, let a be a non zero real number satisfying the equation 3a − (3/a) − 3 = 0. Using this condition, evaluate the expression a^3 − (1/a^3) + 2 exactly.

Accepted Answer

Introduction / Context: This question links a rational equation in a with an expression involving higher powers of a and its reciprocal. Instead of solving for a numerically and then computing a^3 − 1/a^3, it is more efficient to rearrange the given equation to obtain a simpler relationship, and then use standard identities for cubes and reciprocals. This style of question is common in algebraic manipulation sections of aptitude exams. Given Data / Assumptions: - a is a non zero real number, so 1/a is well defined. - The equation 3a − (3/a) − 3 = 0 holds exactly. - We are required to find the exact value of a^3 − 1/a^3 + 2. - Standard algebraic identities and operations on fractions apply. Concept / Approach: First, rearrange the given equation to obtain a relation between a and 1/a. Multiplying through by a removes the denominator and gives a quadratic equation in a. Solving this quadratic yields possible values of a, but we do not need to compute them explicitly. Instead, we can use the relation derived from the quadratic to compute a − 1/a and then a^3 − 1/a^3 using the identity a^3 − 1/a^3 = (a − 1/a)(a^2 + a·(1/a) + 1/a^2). Finally, adding 2 gives the target expression. Step-by-Step Solution: 1) Start from 3a − (3/a) − 3 = 0. 2) Multiply the entire equation by a (which is non zero) to clear the denominator: 3a^2 − 3 − 3a = 0. 3) Rearrange to obtain 3a^2 − 3a − 3 = 0. Divide by 3 to simplify: a^2 − a − 1 = 0. 4) This quadratic shows that a satisfies a^2 = a + 1. 5) From a^2 − a − 1 = 0, we can write 1/a = a − 1 by dividing both sides of a^2 − a − 1 = 0 by a. 6) Therefore, a − 1/a = a − (a − 1) = 1. 7) Use the identity a^3 − 1/a^3 = (a − 1/a)(a^2 + a·(1/a) + 1/a^2). We already have a − 1/a = 1. 8) From a^2 = a + 1 and 1/a = a − 1, we get 1/a^2 = (a − 1)^2 = a^2 − 2a + 1 = (a + 1) − 2a + 1 = 2 − a. 9) Compute a^2 + a·(1/a) + 1/a^2 = (a + 1) + 1 + (2 − a) = a + 1 + 1 + 2 − a = 4. 10) Therefore a^3 − 1/a^3 = (a − 1/a) · 4 = 1 · 4 = 4. 11) Finally, a^3 − 1/a^3 + 2 = 4 + 2 = 6. Verification / Alternative check: We can explicitly solve the quadratic a^2 − a − 1 = 0 to find a = (1 ± √5) / 2. Substituting either root into 3a − 3/a − 3 shows that the original equation holds. Then, using a symbolic calculation, we can verify that a^3 − 1/a^3 is 4 for each root, so adding 2 always yields 6. Since both roots give the same value for the target expression, our identity based method is confirmed as correct. Why Other Options Are Wrong: Option B (4) is the value of a^3 − 1/a^3 before adding 2. Option C (2) and Option D (0) correspond to incomplete use of identities or mis applying the quadratic relation. Option E (−2) would require a^3 − 1/a^3 to be −4, which contradicts the derived relationship. Only Option A matches the completely simplified value of a^3 − 1/a^3 + 2. Common Pitfalls: Some learners try to solve for a numerically and then approximate the expression, which is more work and prone to rounding errors. Others may incorrectly manipulate the equation 3a − 3/a − 3 = 0, for example by dropping the 3 or mis multiplying by a. It is also easy to forget the +2 at the end after finding a^3 − 1/a^3. Keeping track of each transformation and using identities systematically helps avoid mistakes. Final Answer: Using the quadratic relation a^2 − a − 1 = 0 and cube identities, we find that a^3 − 1/a^3 + 2 = 6.

Question 16

In a rhombus, the smaller diagonal is equal to the length of each of its sides. If the length of each side is 4 cm, then the smaller diagonal is 4 cm. Using this information, what is the area (in square centimetres) of an equilateral triangle whose …

Accepted Answer

Introduction / Context: This question combines properties of a rhombus with the area formula for an equilateral triangle. It tests understanding of how diagonals relate to the side of a rhombus and how to use these diagonals to derive the side of a new geometric figure, in this case an equilateral triangle whose side equals the longer diagonal of the rhombus. Given Data / Assumptions: The quadrilateral is a rhombus with all four sides equal in length. The length of each side is 4 cm. The smaller diagonal of the rhombus is equal to the side length, so the smaller diagonal is 4 cm. The longer diagonal is unknown and must be calculated. An equilateral triangle is constructed with side equal to this longer diagonal, and we must find its area in square centimetres. Concept / Approach: For any rhombus, the diagonals are perpendicular bisectors of each other. Each side of the rhombus forms the hypotenuse of a right triangle whose legs are half of each diagonal. If we denote the diagonals by d1 and d2, then side^2 = (d1/2)^2 + (d2/2)^2. After finding the larger diagonal, we use the standard formula for the area of an equilateral triangle: Area = (sqrt(3)/4) * side^2. Step-by-Step Solution: Let the smaller diagonal be d1 = 4 cm and the larger diagonal be d2 cm.Half diagonals are d1/2 = 2 cm and d2/2 cm. The side of the rhombus is 4 cm and is the hypotenuse of the right triangle formed by these halves.Use Pythagoras theorem: side^2 = (d1/2)^2 + (d2/2)^2, so 4^2 = 2^2 + (d2/2)^2.This gives 16 = 4 + d2^2/4, so d2^2/4 = 12 and therefore d2^2 = 48. Hence d2 = 4sqrt(3) cm.The equilateral triangle has side a = d2 = 4sqrt(3). Its area is (sqrt(3)/4) * a^2 = (sqrt(3)/4) * 48 = 12sqrt(3) square centimetres. Verification / Alternative check: The relationship between side and diagonals in a rhombus is consistent for any rhombus: if one diagonal equals the side, the other diagonal must be longer and determined by Pythagoras theorem. The computed longer diagonal d2 = 4sqrt(3) is greater than 4, which is reasonable. Substituting this value into the equilateral triangle area formula matches the simplified exact value 12sqrt(3). No contradictions arise, confirming the result. Why Other Options Are Wrong: 6 and 12 are too small and ignore the factor of sqrt(3) arising from the equilateral triangle formula. 9sqrt(3) would correspond to a smaller effective side length and does not match d2^2 = 48. 18 is a plain integer and cannot be the exact area of an equilateral triangle with an irrational side length 4sqrt(3). Common Pitfalls: Forgetting that the diagonals of a rhombus are perpendicular bisectors and misusing Pythagoras theorem. Using full diagonals instead of half diagonals when setting up the right triangle relation. Applying the wrong area formula for the equilateral triangle or missing the factor sqrt(3)/4. Final Answer: 12√3

Question 17

If the trigonometric equation 2 cos θ = 2 − sin θ holds for an angle θ in a range where both sine and cosine are defined, what are the possible values of cos θ that satisfy this relationship?

Accepted Answer

Introduction / Context: This question tests algebraic manipulation of trigonometric equations and the use of the basic identity sin^2θ + cos^2θ = 1. You are asked to solve the given equation for cos θ and determine all possible values that satisfy both the equation and the fundamental trigonometric identity. Given Data / Assumptions: The equation is 2 cos θ = 2 − sin θ. The angle θ is such that sin θ and cos θ are both defined. We must find the possible values of cos θ that satisfy the equation and the identity sin^2θ + cos^2θ = 1. We assume standard real valued trigonometric functions. Concept / Approach: We treat sine and cosine as algebraic variables linked by the identity sin^2θ + cos^2θ = 1. From the equation 2 cos θ = 2 − sin θ, we express cos θ in terms of sin θ, then substitute this into the identity. This produces a quadratic equation in sin θ, which we solve to find possible sine values. For each sine value, we then use the original equation to find the corresponding cos θ values. Step-by-Step Solution: Start from 2 cos θ = 2 − sin θ and divide by 2: cos θ = 1 − (sin θ)/2.Let s = sin θ. Then cos θ = 1 − s/2. Use the identity sin^2θ + cos^2θ = 1, which becomes s^2 + (1 − s/2)^2 = 1.Expand (1 − s/2)^2: this is 1 − s + s^2/4. So the equation is s^2 + 1 − s + s^2/4 = 1.Combine like terms: s^2 + s^2/4 = (5/4)s^2. So (5/4)s^2 − s + 1 = 1, which simplifies to (5/4)s^2 − s = 0.Factor: s((5/4)s − 1) = 0, giving s = 0 or s = 4/5. For s = 0, 2 cos θ = 2, so cos θ = 1. For s = 4/5, 2 cos θ = 2 − 4/5 = 6/5, so cos θ = 3/5. Verification / Alternative check: Check each candidate pair (sin θ, cos θ) against the identity. For sin θ = 0 and cos θ = 1, we have sin^2θ + cos^2θ = 0 + 1 = 1, which is correct. For sin θ = 4/5 and cos θ = 3/5, sin^2θ + cos^2θ = (16/25) + (9/25) = 25/25 = 1, also correct. Substituting back into the original equation 2 cos θ = 2 − sin θ confirms that both cos θ = 1 and cos θ = 3/5 satisfy the equation. Why Other Options Are Wrong: Options involving −1 or −1/2 suggest sine values that either violate the equation 2 cos θ = 2 − sin θ or the identity sin^2θ + cos^2θ = 1. Option e, 3/5 only, ignores the valid solution cos θ = 1, which is obtained when sin θ = 0. Combinations like 1 or −1/2 and −1 or 3/5 are not supported by the algebraic derivation. Common Pitfalls: Squaring the equation incorrectly or forgetting to apply the identity sin^2θ + cos^2θ = 1. Dropping one of the solutions from the quadratic equation in sin θ. Failing to check the obtained sine and cosine values against both the identity and the original equation. Final Answer: 1 or 3/5

Question 18

The polynomial x^3 + 2x^2 − 5x + k is exactly divisible by x + 1 for all real x. Using the Remainder Theorem or factor theorem, what is the value of the constant term k that makes this divisibility possible?

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Introduction / Context: This question focuses on polynomial division and the use of the Remainder Theorem. When a polynomial is divisible by a linear factor like x + 1, the remainder must be zero when x is replaced by the value that makes the factor equal to zero. Here, we use that idea to determine the constant k in the given cubic polynomial. Given Data / Assumptions: The polynomial is f(x) = x^3 + 2x^2 − 5x + k. The polynomial is exactly divisible by x + 1. Exact divisibility means the remainder is zero when dividing by x + 1. We assume real coefficients and real arithmetic. Concept / Approach: The Remainder Theorem states that if a polynomial f(x) is divided by (x − a), the remainder is f(a). Here, the factor is x + 1, which can be written as x − (−1). Therefore, the remainder when f(x) is divided by x + 1 is f(−1). Exact divisibility implies that this remainder is zero. So we set f(−1) = 0 and solve the resulting equation for k. Step-by-Step Solution: Write the polynomial as f(x) = x^3 + 2x^2 − 5x + k.For division by x + 1, use a = −1. Compute f(−1): f(−1) = (−1)^3 + 2(−1)^2 − 5(−1) + k.Calculate each term: (−1)^3 = −1, 2(−1)^2 = 2, and −5(−1) = 5.So f(−1) = −1 + 2 + 5 + k = 6 + k.Exact divisibility requires f(−1) = 0, so 6 + k = 0. Hence k = −6. Verification / Alternative check: We can verify by substituting k = −6 back into the polynomial and performing synthetic division or direct substitution. With k = −6, f(−1) becomes −1 + 2 + 5 − 6 = 0, confirming the remainder is zero. Alternatively, synthetic division of x^3 + 2x^2 − 5x − 6 by x + 1 will yield a quotient with no remainder, which confirms that x + 1 is indeed a factor when k = −6. Why Other Options Are Wrong: Values like −1, 0, 2, or 6 produce non zero remainders when substituted into f(−1), so the polynomial is not exactly divisible by x + 1 for those choices. Only k = −6 makes the remainder vanish, satisfying the divisibility condition. Common Pitfalls: Confusing the sign when substituting x = −1 into the polynomial. Forgetting that the divisor x + 1 corresponds to evaluating the polynomial at x = −1, not at x = 1. Making arithmetic errors while combining terms, which could lead to an incorrect value of k. Final Answer: -6

Question 19

Given that 3x + 1/(5x) = 7 for a non zero real number x, what is the simplified value of the algebraic expression 5x / (15x^2 + 15x + 1)?

Accepted Answer

Introduction / Context: This question tests your ability to manipulate algebraic expressions using a given relation. Instead of solving directly for x, you can transform the target expression using the original equation and algebraic identities, which is a common technique in aptitude exams to avoid solving messy quadratics completely. Given Data / Assumptions: We are given 3x + 1/(5x) = 7. x is a non zero real number, so division by x is valid. We must find the value of E = 5x / (15x^2 + 15x + 1). The answer should be a simplified rational number. Concept / Approach: Rather than solving the equation for x directly, we introduce a substitution to simplify the algebra. Let y = 5x, which allows us to rewrite both the given equation and the target expression in terms of y. Then we use the quadratic equation satisfied by y to simplify the denominator of E. This often leads to cancellation and a simple final value. Step-by-Step Solution: Let y = 5x. Then x = y/5. The given equation becomes 3x + 1/(5x) = 3(y/5) + 1/y = 7.Multiply both sides by 5y to clear denominators: 5y * (3y/5 + 1/y) = 7 * 5y, which gives 3y^2 + 5 = 35y.Rearrange to form a quadratic: 3y^2 − 35y + 5 = 0. Thus y satisfies this equation.Now rewrite E in terms of y. First note that 15x^2 + 15x + 1 with x = y/5 becomes 15(y^2/25) + 15(y/5) + 1 = (3/5)y^2 + 3y + 1.So E = 5x / (15x^2 + 15x + 1) = y / ((3/5)y^2 + 3y + 1). Multiply numerator and denominator by 5 to get E = 5y / (3y^2 + 15y + 5).Use the quadratic 3y^2 − 35y + 5 = 0 to replace 3y^2 by 35y − 5. Then the denominator becomes (35y − 5) + 15y + 5 = 50y.Thus E = 5y / (50y) = 1/10, since y is non zero. Verification / Alternative check: We can approximate a numerical solution. Solve 3x + 1/(5x) = 7 for x using a calculator and then substitute into the original expression 5x / (15x^2 + 15x + 1). When this is done, the value is extremely close to 0.1, which equals 1/10. This confirms the algebraic result and shows that the substitution and simplification steps are consistent. Why Other Options Are Wrong: 1/5 and 2/5 are larger than the true value and would result from incomplete simplification or misuse of the quadratic relation. 10 and 5/2 are far too large and indicate a serious algebraic error such as inverting the fraction incorrectly. Only 1/10 matches the simplified result derived from consistent algebraic manipulation. Common Pitfalls: Trying to solve directly for x, which leads to complicated algebra instead of a neat substitution. Making errors while transforming the denominator 15x^2 + 15x + 1 into an expression in y. Forgetting to use the quadratic relation 3y^2 − 35y + 5 = 0 to simplify the denominator. Final Answer: 1/10

Question 20

Given that x + 1/(4x) = 5/2 for a non zero real number x, what is the exact value of the expression (64x^6 + 1) / (8x^3), simplified as a single real number?

Accepted Answer

Introduction / Context: This question checks your ability to use algebraic identities and clever substitutions rather than solving directly for x. The given relation x + 1/(4x) = 5/2 helps transform a higher power expression into something simpler. Recognising patterns such as u + 1/u and using them correctly is a common technique in aptitude level algebra. Given Data / Assumptions: We know x + 1/(4x) = 5/2. x is a non zero real number. We must evaluate E = (64x^6 + 1) / (8x^3). The answer should be an exact numerical value. Concept / Approach: Notice that 64x^6 is (8x^3)^2, so the expression (64x^6 + 1) / (8x^3) can be rewritten in the form (u^2 + 1)/u where u = 8x^3. That simplifies to u + 1/u. The given relation involves x and 1/(4x). We can manipulate this relation to obtain x^3 + 1/(64x^3), which is directly related to u + 1/u, because u = 8x^3 and 1/u = 1/(8x^3). Step-by-Step Solution: Let a = x + 1/(4x). We are given a = 5/2.Compute a^2: a^2 = x^2 + 1/(16x^2) + 2 * x * 1/(4x) = x^2 + 1/(16x^2) + 1/2.So x^2 + 1/(16x^2) = a^2 − 1/2 = 25/4 − 1/2 = 25/4 − 2/4 = 23/4.Now consider the product (x^2 + 1/(16x^2)) * (x + 1/(4x)) = x^3 + 1/(64x^3) + x/4 + 1/(16x).Notice x/4 + 1/(16x) = (1/4)(x + 1/(4x)) = a/4. Hence the product equals x^3 + 1/(64x^3) + a/4.So x^3 + 1/(64x^3) = a(x^2 + 1/(16x^2)) − a/4 = a(23/4) − a/4 = a * (22/4) = (11/2) * (5/2) = 55/4.Set u = 8x^3. Then x^3 + 1/(64x^3) = (1/8)(u + 1/u). Thus (1/8)(u + 1/u) = 55/4, so u + 1/u = 8 * 55/4 = 110.Finally, E = (64x^6 + 1) / (8x^3) = (u^2 + 1)/u = u + 1/u = 110. Verification / Alternative check: If you solve x + 1/(4x) = 5/2 explicitly for x, you will obtain two possible real values. Substituting those values back into E using a calculator will show that E is 110 in both cases. This confirms that the algebraic manipulations and the identity based approach are correct and independent of which valid x is chosen. Why Other Options Are Wrong: 115, 125, 140, and 150 correspond to rough or incorrect approximations that arise when identities are misused or some steps are omitted. Only 110 matches the exact expression u + 1/u derived from the given relation. Common Pitfalls: Not spotting that 64x^6 is (8x^3)^2 and missing the chance to rewrite the expression as u + 1/u. Squaring a = x + 1/(4x) incorrectly or forgetting the middle term 1/2. Errors while organising terms to get x^3 + 1/(64x^3) and then relating it to u + 1/u. Final Answer: 110

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