Question:
If $x=1$ is a critical point of the function $f(x)=\left(3 x^{2}+a x-2-a\right) e^{x}$, then :
Correct Option: , 4
Solution:
The given function
$f(x)=\left(3 x^{2}+a x-2-a\right) e^{x}$
$f^{\prime}(x)=(6 x+a) e^{x}+\left(3 x^{2}+a x-2-a\right) e^{x}$
$f^{\prime}(x)=\left[3 x^{2}+(a+6) x-2\right] e^{x}$
$\because x=1$ is critical point:
$\therefore f^{\prime}(1)=0$
$\Rightarrow(3+a+6-2) \cdot e=0$
$\Rightarrow a=-7$ $(\because e>0)$
$\therefore f^{\prime}(x)=\left(3 x^{2}-x-2\right) e^{x}$
$=(3 x+2)(x-1) e^{x}$
\begin{tabular}{c}
$+_{1}-_{1}+$ \\
\hline$-2 / 3 \quad 1$
\end{tabular}
$\therefore x=-\frac{2}{3}$ is point of local maxima.
and $x=1$ is point of local minima.