Question

Diketahui sin 1/2 alpha = 1/2, 0° < alpha < 90°, cos alpha = ?

Answer 1

Sin 1/2 α = sin 30
1/2 α = 30 + k.360
α = 60 + k.720
k = 0 ---> α = 60
yang memenuhi α = 60
sehingga cos α = cos 60' = 1/2