Question

If the value of $\cos \frac{2\pi }{7}+\cos \frac{4\pi }{7}+\cos \frac{6\pi }{7}+\cos \frac{7\pi }{7}=-\frac{\ell }{2}$. Find the value of $\ell$.

Answer 1

Answer: 3

Correct answer is (c)