Question

$f\left(x\right)=|4x|-2x^3$. Find the value of $a$ such that $f\left(a\right)=66$.

• A. $-6$
• B. $-4$
• C. $-3$
• D. $3$
• E. $6$

Answer 1

The correct option is C $-3$

Given, $f\left(x\right)=|4x|-2x^3$
$\Rightarrow f\left(a\right)=|4a|-2a^3=66$
Let us consider that $a$ is negative, we get
$\Rightarrow -4a-2a^3=66$

$\Rightarrow 2a+a^3=-33$
$\Rightarrow a^3+2a+33=0$, we get $-3$ as one root
So, the answer is option $C$.