Bentuk paling sederhana dari 1.Cos 100°+cos 20° 2.cos35°-cos25°

Trigonometri

1.
cos 100 + cos 20 = 2 cos 1/2 (100+20) cos 1/2(100-20)
= 2 cos 60 cos 40
= 2 (1/2)(cos 40)
= cos 40

2.
cos 35 - cos 25 = - 2 sin 1/2(35+25) sin 1/2(35-25)
= - 2 sin 30 sin 5
= -2(1/2) sin 5
= - sin 5