Question

The value of $\cos 0+\cos \frac{\pi}{9}+\cos \frac{2 \pi}{9}+\cos \frac{3 \pi}{9}+\cos \frac{4 \pi}{9}+\cos \frac{5 \pi}{9}+\cos \frac{6 \pi}{9}+\cos \frac{7 \pi}{9}+\cos \frac{8 \pi}{9}$ is

• A. $\frac{1}{2}$
• B. $-\frac{1}{2}$
• C. 0
• D. 1

Answer 1

Answer: (D)

$1+\cos \frac{\pi}{9}+\cos \frac{2 \pi}{9}+\cos \frac{3 \pi}{9}+\cos \frac{4 \pi}{9}-\cos \frac{4 \pi}{9}-\cos \frac{3 \pi}{9}-\cos \frac{2 \pi}{9}-\cos \frac{\pi}{9}=1$