The value of $\cot \frac{\pi }{20}\cot \frac{3\pi }{20}\cot \frac{5\pi }{20}\cot \frac{7\pi }{20}\cot \frac{9\pi }{20}$ is--------

 $\left[\cot \frac{\pi }{20}\cot \frac{9\pi }{20}\right]\left[\cot \frac{3\pi }{20}\cot \frac{7\pi }{20}\right]\cot \left(\frac{5\pi }{20}\right)$
 $(\cot \frac{\pi }{20}\cot \frac{\pi }{2}-\frac{\pi }{20})\left(\cot \left(\frac{3\pi }{20}\right)\cot (\frac{\pi }{2}-\frac{3\pi }{20})\right)\cot \frac{\pi }{4}=\mathrm{1.1.1}=1$