Question

(sin 20°- cos 110°) (sin 20° + cos 110°) sama dengan...

Answer 1

Sin 20 = cos 70
(sin 20 - cos 110) (sin 20 + cos 110)
= (cos 70 - cos 110) (cos 70 + cos 110)
= (-2 sin (70+110)/2 sin (70-110)/2 ) (2 cos (70+110)/2 cos (70-110)/2)
= -2 sin 90 sin (-20) . 2 cos 90 cos (-20)
= -2 . 1 . sin (-20) . 2 . 0 . cos (-20)
= 0