cos2 (120° - A) + cos2 A + cos2 (120°+A) is equal to ?
Answer & explanation
Correct answer: option 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 = -\(\frac{1}{2}\)