Hp dari 3 cos^2 x = sin^2 x Help

3 cos²x = sin²x
3cos²x = 1- cos²x
4cos²x = 1
cos² x = ¼
cos x = ±½

cos x = ½
x = {60°, 300°}

cos x = -½
x= { 120°, 240°}

Hp:{60°,120°,240°,300°}