Diberikan sin a = -12/13 dengan a dikuadran ke 3 hitunglah cos a/2

Trigonometri

a pd kuadran 3 → sin dan cos negatif

sin a = -12/13
cos a = √(1 - sin² a) = -5/13

cos a = cos 2(1/2 a)
cos a = 2 cos² (1/2 a) - 1

cos a = -5/13
2 cos² (1/2 a) - 1 = - 5/13
2 cos² (1/2 a) = 1 - 5/13
cos² (1/2 a) = (8/13) / 2
cos² (1/2 a) = 8/26 = 4/13
cos (1/2 a) = √(4/13)
cos (1/2 a) = 2/13 √13