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
- -2
- 1
- 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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