MCQ
The value of integral $\int_{1/\pi }^{2/\pi } {\frac{{\sin (1/x)}}{{{x^2}}}} \,dx = $
  • A
    $2$
  • B
    $ - 1$
  • C
    $0$
  • $1$

Answer

Correct option: D.
$1$
d
(d) Put $t = \frac{1}{x} $

$\Rightarrow dt = - \frac{1}{{{x^2}}}dx$

as $t = \frac{\pi }{2}$ and $\pi $

$\therefore $ $\int_{1/\pi }^{2/\pi } {\frac{{\sin \left( {\frac{1}{x}} \right)}}{{{x^2}}}dx} $

$ = - \int_{\pi /2}^\pi {\sin t\,dt = - [\cos t]_{\pi /2}^\pi } $

$ = - \left[ {\cos \pi - \cos \left( {\frac{\pi }{2}} \right)} \right] = 1$.

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