A) \[-1\]
B) \[\frac{1}{2}\]
C) 0
D) 1
Correct Answer: D
Solution :
| [d] \[\cot \frac{\pi }{20}\cot \frac{3\pi }{20}\cot \frac{5\pi }{20}\cot \frac{7\pi }{20}\cot \frac{9\pi }{20}\] \[=\cot \frac{\pi }{20}\cot \frac{3\pi }{20}\cot \frac{5\pi }{20}\cot \left( \frac{\pi }{2}-\frac{3\pi }{20} \right)\] \[\cot \left( \frac{\pi }{2}-\frac{\pi }{20} \right)\] \[=\cot \frac{\pi }{20}\cot \frac{3\pi }{20}\cot \frac{5\pi }{20}\tan \frac{3\pi }{20}\tan \frac{\pi }{20}\] \[=\cot \frac{5\pi }{20}=1\] |
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