Tolong bantu jawab yaaa.. Jangan ngasal!! Pake cara!! Terimakasih sebelumnya :)

3cos² 2x + 4cos 2x - 4 = 0
(3cos 2x - 2)(cos 2x + 2) = 0
yg mungkin/memenuhi :
3 cos 2x - 2 = 0
cos 2x = 2/3
2cos² x - 1 = 2/3
cos² x = (2/3 + 1)/2
cos² x = 5/6
cos x = ± √(5/6)
cos x = ± 1/6 √30

Opsi : E