Directions: Solve the quadratic and answer the following questions. A : $(x-2)^2 = (-3x^2) + 2^2 + 25x - P$ B: $\left(10y^2 - 3^2y + \frac{2}{3}\right) \times 3 + 10y = 0$ One root of equation A is $5$. Which of the following are the smallest root of equation A and largest root of equation B-respectively?
Aptitude
Quadratic Equation
Difficulty: Medium
Choose an option
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A$\frac{9}{4}, \frac{2}{5}$
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B$\frac{2}{5}, 5$
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C$\frac{9}{4}, \frac{1}{6}$
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D$\frac{2}{3}, \frac{3}{5}$
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ENone of the above
Answer
Correct Answer: $\frac{9}{4}, \frac{2}{5}$
Explanation
### Concept & Factorization
We need to determine the roots for both Equation A and Equation B. After finding all roots, we simply compare them to select the smallest root from A and the largest root from B.
$$ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} $$
### Step-by-Step Solution
1. **Find roots of Equation A:**
As derived previously, Equation A simplifies to $4x^2 - 29x + 45 = 0$.
The roots are $x = 5$ and $x = \frac{9}{4}$ (or $2.25$).
The smallest root of Equation A is $\frac{9}{4}$.
2. **Simplify Equation B:**
$\left(10y^2 - 3^2y + \frac{2}{3}\right) \times 3 + 10y = 0$
Expand the equation by multiplying by $3$:
$30y^2 - 27y + 2 + 10y = 0$
$30y^2 - 17y + 2 = 0$
3. **Find roots of Equation B:**
Factorize by splitting the middle term. We need two numbers that multiply to $(30 \times 2 = 60)$ and add to $-17$. These are $-12$ and $-5$.
$30y^2 - 12y - 5y + 2 = 0$
$6y(5y - 2) - 1(5y - 2) = 0$
$(6y - 1)(5y - 2) = 0$
The roots are $y = \frac{1}{6}$ and $y = \frac{2}{5}$.
4. **Identify the largest root of Equation B:**
Compare $\frac{1}{6}$ (approx $0.166$) and $\frac{2}{5}$ (which is $0.4$).
The largest root of Equation B is $\frac{2}{5}$.
5. **Combine the results:**
Smallest root of A = $\frac{9}{4}$.
Largest root of B = $\frac{2}{5}$.
Respectively, the values are $\frac{9}{4}, \frac{2}{5}$.
### Exam Strategy & Shortcut
For Equation B, once you reach $30y^2 - 17y + 2 = 0$, you can find the roots using the shortcut of changing the signs of the split middle terms and dividing by $a$: The split terms are $-12, -5$. Change signs: $12, 5$. Divide by $30$: $\frac{12}{30}, \frac{5}{30} \implies \frac{2}{5}, \frac{1}{6}$.
### Common Pitfall
Be careful when comparing fractions. Students sometimes assume that a larger denominator implies a larger number, mistakenly choosing $\frac{1}{6}$ over $\frac{2}{5}$. Always convert to decimals or cross-multiply to verify.
### Final Answer
Therefore, the correct answer is **$\frac{9}{4}, \frac{2}{5}$**.