cos2 (120° - A) + cos2 A + cos2 (120°+A) is equal to ?

\(\frac{1}{2}\)  -1\(\frac{1}{2}\) 0 1

-1\(\frac{1}{2}\)

Let A = 60° cos2 (120°-60°) + cos2 (60°) + cos2 (180°) = cos2 60° + cos2 60° + cos2 180° = \(\frac{1}{4}\) × 2 - 1= \(\frac{1}{2}\)  - 1 =  -\(\frac{1}{2}\)