The value of sin2 15° + sin2 20° + sin2 25° + ….. + sin2 75° --- — Answer & Discussion

The value of sin²15° + sin2 20° + sin²25° + ….. + sin²75° ---

Atan²15° + sin²20° + tan²25° + …. tan²75°
Bcos²15° + cos²20° + cos²25° + …. cos²75°
Ccot²15°+ cot²20° + cot²25° + …. cot²75°
Dsec²15°+ sec²20° + sec²25° + …. sec²75°

Answer not set

Discussion 1

CCommunity13 May 2019

sin2 15° + sin2 20° + sin2 25° + ..... sin2 75°

= [cos (90° - 15°)]2 + [cos (90° - 20°)]2 + ..... [cos (90° - 75°)]2 [cos (90 - θ) = sinθ]

= cos2 75° + cos2 70° + cos2 65° + ...... cos2 15°

= cos2 15° + cos2 20° + cos2 25° + ..... cos2 75°