MCQ
The value of $\int_a^{a + (\pi /2)} {({{\sin }^4}x + {{\cos }^4}x)\,dx} $ is
  • A
    Independent of $a$
  • B
    $a\,{\left( {\frac{\pi }{2}} \right)^2}$
  • $\frac{{3\pi }}{8}$
  • D
    $\frac{{3\pi {a^2}}}{8}$

Answer

Correct option: C.
$\frac{{3\pi }}{8}$
c
(c) Since ${\sin ^4}x + {\cos ^4}x$ is a periodic function with period $\frac{\pi }{2},$

therefore $\int_a^{a + (\pi /2)} {({{\sin }^4}x + {{\cos }^4}x){\rm{ }}dx} $

$ = \int_0^{\pi /2} {({{\sin }^4}x + {{\cos }^4}x)dx} $

$ = 2\int_0^{\pi /2} {{{\sin }^4}x\,dx = \frac{{3\Gamma (5/2)\Gamma (1/2)}}{{2\Gamma \left( {\frac{{4 + 0 + 2}}{2}} \right)}} = \frac{{3\pi }}{8}} $.

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