MCQ
Let a function $h(x)$ be defined as $h(x) = 0$, for all $x \ne 0$. Also $\int\limits_{ - \,\infty }^\infty  {{\rm{h}}(x)\,\cdot\,{\rm{f}}(x)\,dx} $ $= f (0)$, for every function $f (x)$. Then the value of the definite integral $\int\limits_{ - \,\infty }^\infty  {{\rm{h}}'(x)\,\cdot\,\sin x\,dx} $, is
  • A
    equal to zero
  • B
    equal to $1$
  • equal to $- 1$
  • D
    non existent

Answer

Correct option: C.
equal to $- 1$
c
$I =$  $\int\limits_{ - \,\infty }^\infty  {\underbrace {{\rm{h}}'(x)}_{II}\,\cdot\,\underbrace {\sin x}_I\,dx} $ $= \sin x\,\cdot\,\left. {h(x)} \right]_{ - \,\infty }^{\,\infty }$ $- \int\limits_{ - \,\infty }^\infty  {\cos x\,\cdot\,h(x)\,dx} $ $= 0 - \cos \,0 = - 1$
note that here $\cos\, x = f (x)$

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