please bantuannya buat ukk besok

nomer 12 gini
sin a = 4/5
dr identitas trigono diket sin^2 a + cos ^2 a = 1
maka cos^2 a = 1 - sin^2 a
cos^2 a = 1 - (4/5)^2
cos^2 a = 1 - 16/25
cos^2 a = 25/25 - 16/25
cos^2 a = 9/25
cos a = akar 9/25
cos a = 3/5 (positif di kuadran I)