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MHT CET · Maths · Inverse Trigonometric Functions

If \(\cot ^{-1}(\sqrt{\cos \alpha})-\tan ^{-1}(\sqrt{\cos \alpha})=x\), then the value of \(\sin x\) is

  1. A \(\cot ^2\left(\frac{\alpha}{2}\right)\)
  2. B \(\tan ^2\left(\frac{\alpha}{2}\right)\)
  3. C \(\tan \alpha\)
  4. D \(\cot \left(\frac{\alpha}{2}\right)\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(\tan ^2\left(\frac{\alpha}{2}\right)\)

Step-by-step Solution

Detailed explanation

\(\begin{gathered}\cot ^{-1}(\sqrt{\cos \alpha})-\tan ^{-1}(\sqrt{\cos \alpha})=x \\ \Rightarrow \tan ^{-1}\left[\frac{1}{\sqrt{\cos \alpha}}\right]-\tan ^{-1}[\sqrt{\cos \alpha}]=x \\ \Rightarrow \tan ^{-1}\left[\frac{\frac{1}{\sqrt{\cos \alpha}}-\sqrt{\cos \alpha}}{1+\frac{\sqrt{\cos \alpha}}{\sqrt{\cos \alpha}}}\right]=x \\ \Rightarrow \tan x=\frac{1-\cos \alpha}{2 \sqrt{\cos \alpha}} \\ \therefore \quad \sin x=\frac{1-\cos \alpha}{1+\cos \alpha}=\frac{2 \sin ^2 \frac{\alpha}{2}}{2 \cos ^2 \frac{\alpha}{2}} \\ \quad=\tan ^2\left(\frac{\alpha}{2}\right)\end{gathered}\)