Question

prove cos x + cos(120-x) + cos(120+x) = 0​

Answer 1

Answer:

cosx + cos (120-x) + cos (120+x)

=>. cosx + 2cos [(120-x+120+x) /2] cos [(120-x-120-x) /2]

=>. cosx + 2cos120 cos(-x)

=>. cosx + 2cos(180-60) cosx

=>. cosx + 2 (-cos 60) cosx

=>. cosx - 2 × 1/2 cosx

=>. cosx - cosx

=>. 0 hence proved