sin alpha = 1/5 akar 13 alpha sudut lancip nilai cos=?

cos^2 x = 1- sin^2 x
cos^2 x = 1- (13/25)
= 12/25
cos x = 1/5 akar 12

sinα=1/5(√13)
misal segitiga siku2 ABC
sinα=BC/AC
BC=√13
AC=5
AB=√AC²-BC²=√25-13 =2√3
cosα=AB/AC=(2√3)/5