\(\int \frac{d x}{\cos ^2(x)+\sin (2 x)}=\)

\(\int \frac{d x}{\cos ^2(x)+\sin (2 x)}=\)
  1. \(\frac{1}{2} \log |1+2 \cos (x)|+c\)
  2. \(\frac{1}{2} \log |1-2 \tan (x)|+c\)
  3. \(\frac{1}{2} \log |1+2 \tan (x)|+c\)
  4. \(\frac{1}{2} \log |1+2 \cot (x)|+c\)

Solution

\(I=\int \frac{d x}{\cos ^2 x+\sin 2 x}=\int \frac{\sec ^2 x d x}{1+2 \tan x}\) Put \(1+2 \tan x=t \Rightarrow \sec ^2 x d x=\frac{d t}{2}\) So, \(I=\frac{1}{2} \int \frac{d t}{t}=\frac{1}{2} \log _e|t|+C=\frac{1}{2} \log _e|1+2 \tan x|+C\) Hence, option (c) is correct.

Asked in: AP EAMCET 2020 (21 Sep Shift 1)

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