Minta bantuannya yaaa..

Sin a = 6/10
90 < a < 180 = dikuadran 2
Cos a ?
10^2 - 6^2 = b^2
64 = b^2
8 = b
Cos a = 8/10 = 4/5
Karena dikuadran 2, cos bernilai negatif maka
Cos a = - 4/5 (C)