# Given sinx=4/5, cosy = 7/25. Find the following

1. Feb 10, 2009

### Random-Hero-

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

Angles x and y are located in the first quadrant such that sinx=4/5, and cosy = 7/25.

a) Determine an exact value of cosx.

b) Determine an exact value of siny.

c) Determine an exact value for sin(x+y)

2. Relevant equations

Compound angle formulas perhaps? I don't really know, thats the problem!

3. The attempt at a solution

I'm really at a loss here, do I just sub those in to some formula or something? Can anyone help me out? Or get me pointed in the right direction? thanks in advance!!

2. Feb 10, 2009

### Hitman2-2

Let's start with part a). Have you thought about $$sin^2(x) + cos^2(x) = 1$$?

3. Feb 10, 2009

### Random-Hero-

Holy smoke I can't believe I missed that! thanks hitman! I owe you one!

Now for the last 2 lil buggers!

4. Feb 10, 2009

### Random-Hero-

well I got a and b, now how would I do c? :|

5. Feb 10, 2009

### Random-Hero-

Nevermind, I got it, thanks for your help hitman! I don't know how on earth i missed that!!

6. Feb 10, 2009

### HoangFat

sin(x+y) = sinx*cosy+siny*cosx