$\sum\cos=0$ and $\sum\sin=0$ when.......

Question

help me to solve this problem. If $\cos(\beta-\gamma)+\cos(\gamma-\alpha)+\cos(\alpha-\beta)=-\frac{3}{2}$ then show that $\sum\cos=0$ and $\sum\sin=0$

Perhaps it is $\cos(\alpha)+\cos(\beta)+\cos(\gamma)$? Similarly for $\sin$? — Ian Mateus, Dec 18 '13 at 15:28

score 4 · Answer 1 · answered Dec 18 '13 at 15:36

4

Hint: Expand the squares in $$ (\cos\alpha+\cos\beta+\cos\gamma)^2 + (\sin\alpha+\sin\beta+\sin\gamma)^2 $$ and simplify using the usual trigonometric identities.

answered Dec 18 '13 at 15:36

$\sum\cos=0$ and $\sum\sin=0$ when.......

1 Answers1