If the integral $\int \frac{5 \tan x}{\tan x-2} d x=x+a \ln |\sin x-2 \cos x|+k$, then $a$ is equal to

If the integral $\int \frac{5 \tan x}{\tan x-2} d x=x+a \ln |\sin x-2 \cos x|+k$, then $a$ is equal to
  1. $-1$
  2. $-2$
  3. $1$
  4. $2$

Solution

$\int \frac{5 \tan x}{\tan x-2} d x=\int \frac{5 \sin x}{\sin x-2 \cos x} d x$ $\Rightarrow \int\left[\frac{2(\cos x+2 \sin x)+(\sin x-2 \cos x)}{\sin x-2 \cos x}\right] d x$ $=2 \int\left(\frac{\cos x+2 \sin x}{\sin x-2 \cos x}\right) d x+\int d x+k$ $=2 \log |\sin x-2 \cos x|+x+k \quad \therefore a=2$

Asked in: JEE Main 2012 (Offline)

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