hitunglah nilai dari cos 220 + cos 100 +cos 20?

cos 220 + (cos 100 + cos 20) ? = cos 220 + 2 cos 60 cos 40 = cos 220 + 2 (1/2) cos 40 = cos 220 + cos 40 =
+ 2 cos 120 cos 90 =
+ 2 (1/2) (0) = 0