Question

cos^2A+cos^2(A+120)+cos^2(A-120)=3/2 prove
its urgent ....

Answer 1

i hope it will help u

Answer 2

The proof is as follows

Cos 2A = 2Cos2(A) – 1

Cos 2A + 1 = 2 Cos 2 ( A )  

(1 + Cos 2A)  /2 = Cos 2A

i.e  Cos 2A = (1 + Cos 2A)/2

${array}{l}{\frac{1+\cos (2(A-120))}{2}+\cos 2 A+\frac{1+\cos (2(A+120))}{2}}\\ {\frac{1+\cos ((2 A-240))+1+1+\cos ((2 A+240))}{2}+\cos 2 A}\\ {1+\frac{\cos ((2 A-240))+1+1+\cos ((2 A+240))}{2}+\cos 2 A}\\ {1+\frac{2 \cos 2 A \cos 240}{2}+\cos 2 A}{array}$

1 + Cos2 A( -1/2  ) + Cos2 A

1- ( 2 Cos 2A -1) (  1/2  ) + Cos2A

1 – Cos2A + (  1/2  ) + Cos2 A

= 3/2