AP EAMCET · Maths · Trigonometric Ratios & Identities
\(4 \cos \frac{\pi}{7} \cos \frac{\pi}{5} \cos \frac{2 \pi}{7} \cos \frac{2 \pi}{5} \cos \frac{4 \pi}{7}=\)
- A \(-\frac{1}{8}\)
- B \(\frac{1}{32}\)
- C \(-\frac{1}{32}\)
- D \(\frac{1}{8}\)
Answer & Solution
Correct Answer
(A) \(-\frac{1}{8}\)
Step-by-step Solution
Detailed explanation
\begin{aligned} & 4 \cos \left(\frac{\pi}{7}\right) \cos \left(\frac{2 \pi}{7}\right) \cos \left(\frac{4 \pi}{7}\right) \times \cos \left(\frac{\pi}{5}\right) \cos \left(\frac{2 \pi}{5}\right) \\ & \begin{array}{c}=\frac{2}{\sin \left(\frac{\pi}{7}\right)} \sin \left(\frac{2…
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