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

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

Solution

We have, $ \int \frac{5 \tan x}{\tan x-2} d x=x+a \log |\sin x-2 \cos x|+K $ On differentiating, we get $ \begin{aligned} & \frac{5 \tan x}{\tan x-2}=1+\frac{a(\cos x+2 \sin x)}{\sin x-2 \cos x} \\ \Rightarrow \quad \frac{5 \tan x}{\tan x-2} & =1+\frac{a(1+2 \tan x)}{\tan x-2} \\ \Rightarrow \quad & \frac{5 \tan x}{\tan x-2}=\frac{\tan x-2+a+2 a \tan x}{\tan x-2} \\ \Rightarrow \quad 5 \tan x & =(2 a+1) \tan x+a-2 \end{aligned} $ Equating the coefficient of $\tan x$ and constant terms, we get $ \begin{aligned} 2 a+1 & =5 \\ a-2 & =0 \\ \therefore \quad a & =2 \end{aligned} $

Asked in: AP EAMCET 2021 (25 Aug Shift 1)

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