Question

If the function $f\left(x\right)$ = $x^4-62x^2+ax+9$ is maximum at $x=1$, then the value of a is

• A. 120
• B. -120
• C. 52
• D. 128

Answer 1

The correct option is A 120

$f\left(x\right)=x^4-62x^2+ax+9$. Then,

$\frac{d}{dx}f\left(x\right)=4x^3-124x+a$

It is given that f(x) attains its maximum at $x=1$.

Therefore, $\frac{d}{dx}f\left(1\right)=0$

$4-124+a=0$

$a=120$