2010 · Q41
What is the value of sin²15° + sin²20° + sin²25° + ……… + sin²75° ?
Elementary MathematicsTrigonometry
- Atan²15° + tan²20° + tan²25° + … + tan²75°
- Bcos²15° + cos²20° + cos²25° + … + cos²75°
- Ccot²15° + cot²20° + cot²25° + … + cot²75°
- Dsec²15° + sec²20° + sec²25° + … + sec²75°
Explanation
sin²θ+sin²(90°-θ)=1 pairs the sum to cos² sum; both equal 6.5.