MCQ
$\int_{\, - \pi /2}^{\,\pi /2} {{{\sin }^4}x{{\cos }^6}x\,dx = } $
  • A
    $\frac{{3\pi }}{{64}}$
  • B
    $\frac{{3\pi }}{{572}}$
  • $\frac{{3\pi }}{{256}}$
  • D
    $\frac{{3\pi }}{{128}}$

Answer

Correct option: C.
$\frac{{3\pi }}{{256}}$
c
(c) $I = \int_{ - \pi /2}^{\pi /2} {{{\sin }^4}x{{\cos }^6}x\,dx} $

$ = 2\int_0^{^{\pi /2}} {{{\sin }^4}x\,{{\cos }^6}x.\,dx} $

$\begin{matrix}
   \because \int_{-a}^{a}{f(x)\,dx=2\int_{0}^{a}{f(x)\,dx,}} & \text{if }f(-x)=f(x)  \\
   \,\,\,\,\,=0, & \text{if }f(-x)=-f(x)  \\
\end{matrix}$

Applying Gamma function, we get

$I = \frac{{2\,\Gamma 5/2\,.\,\Gamma 7/2}}{{2\,.\Gamma 6}}$

$ = \frac{{3/2.1/2.\sqrt {\pi .} 5/2.3/2.1/2.\sqrt \pi }}{{5.4.3.2.1}}$

$ = \frac{{3\pi }}{{{2^8}}} = \frac{{3\pi }}{{256}}$.

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