Let ∠X and ∠Y be complementary. If sin(X) = 3/5 and cos(X) = 4/5 then what is the value of sin(Y)?

Question

Let ∠X and ∠Y be complementary. If sin(X) = 3/5  and cos(X) = 4/5  then what is the value of sin(Y)?

A)3/5

B) 4/5

C) 5/4

D) 5/3

Is it A?

Reiny · Accepted Answer

x+y = 90 y = 90-x siny = sin(90-x) = cosx = 4/5 the sin( of any angle) = cos(of its complement) the fact that sinx = 3/5 was a distraction and did not have to be given.