JEE Advance - Mathematics (2012 - Paper 2 Offline - No. 10)

If $$f\left( x \right) = \int_0^x {{e^{{t^2}}}} \left( {t - 2} \right)\left( {t - 3} \right)dt$$ for all $$x \in \left( {0,\infty } \right),$$ then
$$f$$ has a local maximum at $$x=2$$
$$f$$ is decreasing on $$(2, 3)$$
there exists some $$c \in \left( {0,\infty } \right),$$ such that $$f'(c)=0$$
$$f$$ has a local minimum at $$x=3$$

Explanation

$$\begin{aligned} & \text { Given, } f(x)=\int_0^x e^{t^2}(t-2)(t-3) d t, x \in(0, \infty) \\ & \Rightarrow \quad f^{\prime}(x)=e^{x^2}(x-2)(x-3) \end{aligned}$$

IIT-JEE 2012 Paper 2 Offline Mathematics - Application of Derivatives Question 73 English Explanation

Here, $$f^{\prime}(x)$$ changes its sign $$+v e$$ to $$-v e$$ about $$x=2$$ and $$f^{\prime}(x)$$ changes its sign $$-v \mathrm{e}$$ to $$+v \mathrm{e}$$ about $$x=3$$

Hence, $$x=2$$ is the point of local maxima and $$x=3$$ is the point of local minima

$$\because f^{\prime}(x)<0$$ for $$x \in(2,3)$$

$$\therefore f(x)$$ is decreasing on $$x \in(2,3)$$

$$\because \quad f^{\prime}(x)$$ is continuous and differentiable for all $$x(0, \infty)$$ and $$f^{\prime}(2)=f^{\prime}(3)=0$$

$$\therefore$$ According to Rolle's theorem, $$f^{\prime \prime}(c)=0$$ must have at least one root $$\in(2,3)$$

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