MCQ
The value of $\int_{-\pi / 2}^{\pi / 2} \frac{\cos ^{2} x}{1+3^{x}} d x$ is
  • $\frac{\pi}{4}$
  • B
    $4 \pi$
  • C
    $\frac{\pi}{2}$
  • D
    $2 \pi$

Answer

Correct option: A.
$\frac{\pi}{4}$
a
$I =\int_{-\pi / 2}^{\pi / 2} \frac{\cos ^{2} x }{1+3^{ x }} dx$ (using king)

$I =\int_{-\pi / 2}^{\pi / 2} \frac{\cos ^{2} x }{1+3^{- x }} dx =\int_{-\pi / 2}^{\pi / 2} \frac{3^{ x } \cos ^{2} x }{1+3^{ x }} dx$

$2 I =\int_{-\pi / 2}^{\pi / 2} \frac{\left(1+3^{ x }\right) \cos ^{2} x }{1+3^{ x }} dx$

$=\int_{-\pi / 2}^{\pi / 2} \cos ^{2} xdx =2 \int_{0}^{\pi / 2} \cos ^{2} x dx$

$\Rightarrow I =\int_{0}^{\pi / 2} \cos ^{2} x dx =\frac{\pi}{4}$

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