For $x \in\left(0, \frac{5 \pi}{2}\right)$, define $f(x)=\int_0^x \sqrt{t} \sin t d t$. Then $f$ has

For $x \in\left(0, \frac{5 \pi}{2}\right)$, define $f(x)=\int_0^x \sqrt{t} \sin t d t$. Then $f$ has
  1. local minimum at $\pi$ and $2 \pi$
  2. local minimum at $\pi$ and local maximum at $2 \pi$
  3. local maximum at $\pi$ and local minimum at $2 \pi$
  4. local maximum at $\pi$ and $2 \pi$

Solution

$f^{\prime}(x)=\sqrt{x} \sin x$ Given $x \in\left(0, \frac{5 \pi}{2}\right)$ $f^{\prime}(x)$ changes sign from +ve to -ve at $\pi$ $f^{\prime}(x)$ changes sign from -ve to +ve at $2 \pi$ $f$ has local max at $\pi$, local min at $2 \pi$

Asked in: JEE Main 2011

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