Question

Prove that cos27°+cos93°+cos147=0

Answer 1

cos 27°+ cos 93°+ cos 147°
2cos (27+93) /2cos(27-93)/2 + cos 147
2 cos 120/2cos66/2 + cos 147
2cos 60cos 33+cos 147
2×1/2×cos 33+cos 147
2cos ( 33+147 )
2cos (33+147) /2cos(33-147) /2
2 cos 180 /2cos 114/2
2cos 90°57°
= 0 ( proved )