cos10+cos110+cos130=0
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As cos (A+B) + cos (A-B) = 2 cos A cos B so putting A + B = 130 and A-B= 110
and getting A = 120 B = 10
we get cos(130) + cos 110 = 2 cos 120 cos 10 = 2*(-1/2) cos 10 = - cos 10
so cos 130 + cos 110 + cos 10 =0
Hence Solved
and getting A = 120 B = 10
we get cos(130) + cos 110 = 2 cos 120 cos 10 = 2*(-1/2) cos 10 = - cos 10
so cos 130 + cos 110 + cos 10 =0
Hence Solved
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