If $f(x)=\int_{0}^{x} e^{t^{2}}(t-2)(t-3) d t$ for all $x \in(0, \infty)$, then

If $f(x)=\int_{0}^{x} e^{t^{2}}(t-2)(t-3) d t$ for all $x \in(0, \infty)$, then
  1. $f$ has a local maximum at $x=2$
  2. $f$ is decreasing on $(2,3)$
  3. there exists some $c \in(0, \infty)$, such that $f^{\prime \prime}(c)=0$
  4. $f$ has a local minimum at $x=3$

Solution

$f(x)=\int_{0}^{x} e^{t^{2}}(t-2)(t-3) d t$ $\Rightarrow f^{\prime}(x)=e^{x^{2}} \cdot(x-2)(x-3)$ Put $f^{\prime}(x)=0 \Rightarrow x=2,3$ $f^{\prime \prime}(x)=e^{x^{2}} \cdot 2 x\left(x^{2}-5 x+6\right)+e^{x^{2}}(2 x-5)$ $f^{\prime \prime}(2)=-$ ve and $f^{\prime \prime}(3)=+$ ve $\therefore \quad x=2$ is a point of local maxima. and $x=3$ is a point of local minima. Also for $x \in(2,3), f^{\prime}(x) < 0$ $\Rightarrow \quad f$ is decreasing on $(2,3)$. Also we observe $f^{\prime \prime}(0) < 0$ and $f^{\prime \prime}(1)>0$ $\therefore \quad$ There exists some $C \in(0,1)$ such that $f^{\prime \prime}(C)=0$ Hence all the options are correct.

Asked in: JEE Advanced 2012 (Paper 2)

Practice more Applications of Derivatives questions on Aicharya