sin a=1/3V5 cos 1/2 a adalah??

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

cos 2(1/2 a) = 2cos² (1/2 a ) - 1)
2 cos² (1/2 a) = cos a + 1
cos² (1/2 a) = (5/3)/2
cos² (1/2 a) = 5/6
cos (1/2 a) = √(5/6)
cos (1/2 a) = 1/6 √30