Tentukan nilai = (Sin 20° – cos 110°) (sin 20°+cos 110°) sama dengan….

Berarti sin 20° = sin (90-70) = cos 70°

(cos 70° – cos 110°) (cos 70° + cos 110°) =
-2 sin (70+110)/2 .sin (70-110/2) 2. cos (70+110)/2 .2 cos (70-110)/2 =
-2 .sin 90. sin -20 .cos 90.2 cos -20 =
-2.1. – sin (20) 0.2. – cos 20 =
0