jika nilai sin 2x =1/3 √5 dan 90° < 2x <180° nilai cos x adapah

Interval : 90° < 2x < 180°
Kuadran II : sin (+) , cos (-)

sin 2x = 1/3 √5

cos 2x = √(1 - sin² 2x)
cos 2x = √(1 - 5/9)
cos 2x = √(4/9)
cos 2x = -2/3

cos 2x = -2/3
2cos² x - 1 = -2/3
2cos² x = 1 - 2/3
cos² x = (1/3)/2
cos² x = 1/6
cos x = √1/6
cos x = 1/6 √6