Question

$1+\cos \frac{\pi }{7}+\cos \frac{2\pi }{7}+\cos \frac{3\pi }{7}+\cos \frac{4\pi }{7}+\cos \frac{5\pi }{7}+\cos \frac{6\pi }{7}=$

• A. 0
• B. 1
• C. 2
• D. 3

Answer 1

Answer: (A)

If $(A+B)=\pi$ then $(\cos A+\cos B)=0$