the value of `cos^2theta+cos^2((2pi)/3-theta)+cos^2((2pi)/3+theta)` is (a)3 (b)`1/2` (c)`3/2` (d)none of these

Prove that : cos^2 theta+ cos^2 ((2pi)/3 -theta) + cos^2 ((2pi)/3 +theta) = 3/2

Prove that cos theta +cos ((2pi)/(3)-theta)+cos ((2pi)/(3)+theta)=0

Prove that cos theta + cos ((2pi)/(3)- theta)+ cos ((2pi)/(3)+ theta)=0

Prove that cos^(2)theta+cos^(2)((2pi)/(3)+theta)+cos^(2)((2pi)/(3)-theta)=(3)/(2)

Prove that: cos^(2)theta+cos^(2)((2 pi)/(3)-theta)+cos^(2)((2 pi)/(3)+theta)=(3)/(2)

Prove that: cos^(2)theta+cos^(2)((pi)/(3)+theta)+cos^(2)((pi)/(3)-theta)=(3)/(2)

cos((3 pi)/(2)+theta)*cos(2 pi+theta)=

Prove that: 2cos theta cos((pi)/(3)+theta)cos((pi)/(3)-theta)=cos3 theta

Prove that cos theta + cos[(2pi)/3 + theta] + cos [(4pi)/(3) + theta] = 0 .

If x/(costheta)=y/(cos(theta-(2pi)/3))=z/(cos(theta+(2pi)/3)) then x+y+z is (a)1 (b) 0 (c) -1 (d) none of these