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TS EAMCET · Maths · Trigonometric Equations

If \(\cot \left(\frac{A}{2}\right)=\sqrt{\frac{1+a}{1-a}} \cdot \cot \left(\frac{\theta}{2}\right)\), then \(\cos \theta=\)

  1. A \(\frac{(\cos A)+a}{1-a \cos A}\)
  2. B \(\frac{(\cos A)-a}{1-\operatorname{acos} A}\)
  3. C \(\frac{(\cos A)-a}{1+a \cos A}\)
  4. D \(\frac{(\cos A)+a}{1+a \cos A}\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(\frac{(\cos A)-a}{1-\operatorname{acos} A}\)

Step-by-step Solution

Detailed explanation

\(\begin{aligned} & \text { We have, } \cot \frac{A}{2}=\sqrt{\frac{1+a}{1-a}} \cot \frac{\theta}{2} \\ & \Rightarrow \quad \cot ^2 \frac{A}{2}=\left(\frac{1+a}{1-a}\right) \cot ^2 \frac{\theta}{2}\end{aligned}\)…