If $x = -1$ and $x = -2$ are the extreme points of $f(x) = a\log|x| + βx^2 +x$ then
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → $α=\frac{2}{3},β=\frac{1}{6}$
Given:
$f(x)=a\log|x|+\beta x^{2}+x$
Extreme points occur where $f'(x)=0$.
Differentiate:
$f'(x)=a\frac{1}{x}+2\beta x+1$
Given that $x=-1$ and $x=-2$ are extreme points, so:
$a\frac{1}{-1}+2\beta(-1)+1=0$
$-a-2\beta+1=0$
(1) $a+2\beta=1$
Next condition:
$a\frac{1}{-2}+2\beta(-2)+1=0$
$-\frac{a}{2}-4\beta+1=0$
(2) $\frac{a}{2}+4\beta=1$
Multiply (1) by 1 and (2) by 1 to solve:
(1) $a+2\beta=1$
(2) $\frac{a}{2}+4\beta=1$
Multiply (2) by 2:
$a+8\beta=2$
Subtract (1) from this:
$a+8\beta - (a+2\beta)=2-1$
$6\beta=1$
$\beta=\frac{1}{6}$
Substitute into (1):
$a+2\left(\frac{1}{6}\right)=1$
$a+\frac{1}{3}=1$
$a=\frac{2}{3}$
The required values are:
$a=\frac{2}{3}$ and $\beta=\frac{1}{6}$