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Question: Answered & Verified by Expert
If $\tan (\cot x)=\cot (\tan x)$, then $\sin 2 x$ is equal to:
MathematicsTrigonometric EquationsBITSATBITSAT 2016
Options:
  • A $\frac{2}{(2 n+1) \pi}$
  • B $\frac{4}{(2 n+1) \pi}$
  • C $\frac{2}{n(n+1) \pi}$
  • D $\frac{4}{n(n+1) \pi}$
Solution:
2620 Upvotes Verified Answer
The correct answer is: $\frac{4}{(2 n+1) \pi}$
Given, $\tan (\cot x)=\cot (\tan x)=\tan \left(\frac{\pi}{2}-\tan x\right)$

$\Rightarrow \cot x=n \pi+\frac{\pi}{2}-\tan x$

$\Rightarrow \cot x+\tan x=n \pi+\frac{\pi}{2}$

$\Rightarrow \frac{1}{\sin x \cos x}=n \pi+\frac{\pi}{2} \Rightarrow \frac{1}{\sin 2 x}=\frac{n \pi}{2}+\frac{\pi}{4}$

$\Rightarrow \sin 2 x=\frac{1}{\frac{n \pi}{2}+\frac{\pi}{4}}=\frac{4}{(2 n+1) \pi}$

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