Question

Jika
, nilai cos 2x = . . . .
bantuin dong pake caranya, buat UTS nih kawan :) makasih

Answer 1

3 cos (x + 30°)  = cos (x - 30°) 
3 cos x cos 30° - 3 sin x sin 30° = cos x cos 30° + sin x sin 30° 
2 cos x cos 30° = 4 sin x sin 30°
2 cos  x. (1/2 √3) = 4 sin x. (1/2)
√3 . cos x = 2 sin x
sin x / cos x = √3 / 2
tan x = √3/ (2)
cos x = 2/√7
cos 2x = 2 cos² x -1 = 2 (2/√7)² -1 = 2(4/7) - 1 = 1/7
sin x sin  / cos x cos 30° =