Prove that:
`cos A +cos (120^o +A) +cos (120^o -A) =0`

cos A + cos (120 ^(@) - A ) + cos (120 ^(@) + A ) =0

Prove that cos theta + cos (120^(@) + theta) + cos ( 120^(@)-theta) =0. Hence deduce that cos ^(3) theta + cos ^(3) ( 120^(@) + theta ) + cos^3( 120^(@)-theta) = 3/4 cos 3 theta.

Prove that : cos 10^(@) + cos 110^(@) + cos 130^(@) = 0 .

cos120^o=

cos210^o=

Prove that: cos Acos(60^0-A)cos(60^0+A)=1/4cos3A

Prove that cos ^(2) A + cos ^(2) (A + 120^(@)) + cos ^(2) (A -120^(@)) = (3)/(2)

Prove that: cos 100^0+cos 20^0=cos 40^0

Prove that: cos 20^0+cos 100^0+cos 140^0=0

Prove that cos^3A+cos^3(120^0+A)+cos^3(240^0+A)=3/4cos3A