47 point sin x = 2 sin 2x dan x sudut lancip berapakah cos 2x ??

Kelas 10 Matematika
Bab Trigonometri

sin x = 2 . sin 2x
sin x = 2 . 2 . sin x . cos x
4 . sin x . cos x = sin x
cos x = sin x/(4 . sin x)
cos x = 1/4

cos 2x = 2 cos² x - 1
cos 2x = 2 . (1/4)² - 1
cos 2x = 2 . 1/16 - 1
cos 2x = 2/16 - 16/16
cos 2x = -14/16
cos 2x = -7/8