Q16Multiple choice
16 16 16 TRIGONOMETRIC FUNCTIONS 49 Solution Correct choice is (C). Indeed sin 20° sin 40° sin 60° sin 80°. 3 3 = sin 20° sin (60° – 20°) sin (60° + 20°) (since sin 60° = ) 2 2 = sin 20° [sin2 60° – sin2 20°] (Why?) 3 3 = sin 20° [ – sin2 20°] 2 4 3 1 = × [3sin 20° – 4sin3 20°] 2 4 3 1 = × (sin 60°) (Why?) 2 4 3 1 3 3 = × × = 2 4 2 16 π 2π 4π 8π