How to Find the Exact Values of Cosine and Sine of Compound Angles

[zeion]

Homework Statement

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

Homework Equations

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