Compound angle homework

[zeion]

1. The problem statement, all variables and given/known data

Angles x and y are located in the first quadrant such that sin x = 3/5 and cos y = 5/13.

a) Determine the exact value for cosx
b) Determine the exact value for siny


2. Relevant equations



3. The attempt at a solution

I don't know what to do.
Am I supposed to do something with the angle a+b?

[Rosengrip]

Use the expression sin2x + cos2x = 1, x being either alpha or beta :) .

[zeion]

oh jeez i feel dumb