Read the following passage and answer the given questions. Two algebraic expressions are given as (I) $6x^2 + 29x + P$ and (II) $3x + 1$. (I) is divided by (II) leaving $(2x + 9)$ as quotient and 19 as remainder. What is the value of largest root of equation $6x^2 + 29x + P = 0$?
Aptitude
Quadratic Equation
Difficulty: Medium
Choose an option
-
A$-1\frac{1}{3}$
-
B$\frac{1}{3}$
-
C$\frac{2}{3}$
-
D$\frac{1}{4}$
-
ENone of these
Answer
Correct Answer: $-1\frac{1}{3}$
Explanation
### Concept & Quadratic Equation Roots
To find the roots of a quadratic equation, we can use factorization by splitting the middle term.
$$ ax^2 + bx + c = 0 $$
### Step-by-Step Solution
* From the previous problem, we found that $P = 28$.
* Substitute $P$ into the equation: $6x^2 + 29x + 28 = 0$.
* To factorize, we need two numbers that multiply to $a \times c$ ($6 \times 28 = 168$) and add to $b$ ($29$).
* These numbers are 21 and 8 ($21 + 8 = 29$ and $21 \times 8 = 168$).
* Split the middle term: $6x^2 + 21x + 8x + 28 = 0$.
* Factor by grouping: $3x(2x + 7) + 4(2x + 7) = 0$.
* This gives $(3x + 4)(2x + 7) = 0$.
* Setting each factor to zero yields the roots: $x = -\frac{4}{3}$ and $x = -\frac{7}{2}$.
* Convert to mixed fractions/decimals to compare: $x = -1\frac{1}{3}$ and $x = -3.5$.
* Since $-1.33$ is greater than $-3.5$, the largest root is $-1\frac{1}{3}$.
### Exam Strategy & Shortcut
Once you have the roots as $-\frac{21}{6}$ and $-\frac{8}{6}$, you can immediately see that $-\frac{8}{6}$ (which simplifies to $-\frac{4}{3}$) is a smaller negative number and thus the larger value. There's no need to convert fully to decimals if you recognize relative fractional sizes.
### Common Pitfall
Choosing $-\frac{7}{2}$ (or $-3.5$) instead of $-1.33$ because $3.5$ is a larger magnitude. Remember that on the negative side of the number line, numbers closer to zero have a larger mathematical value.
### Final Answer
Therefore, the correct answer is **$-1\frac{1}{3}$**.