The value of

Question:

The value of $\int_{-\pi / 2}^{\% / 2} \frac{\cos ^{2} x}{1+3^{x}} d x$ is:

  1. (1) $2 \pi$

  2. (2) $4 \pi$

  3. (3) $\frac{\pi}{2}$

  4. (4) $\frac{\pi}{4}$


Correct Option: , 4

Solution:

Let $I=\int_{-\pi / 2}^{5 / 2} \frac{\cos ^{2} x}{1+3^{x}} d x$

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

$2 I=\int_{-\pi / 2}^{/ 2} \cos ^{2} x d x$

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

 

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