Question

Cosx +cos 120-X+cos 120+X =0

Answer 1

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

L.H.S

cos x+ 2 cos (120-x +120 + x)/2.cos (120- x

-120-x)

[ cos C + cos D = 2 cos (C+D)/2.cos(C-D)/2]

= cos x + 2 cos 120 .cos(-x). [cos120= -1/2]

[cos (-x) = cos x ]

= cos x + 2×-1/2.cosx

= cos x - cos x

= 0

R.H.S

Proved

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Answer 2

hence prove.....

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