# Homework Help: Problem in trigonometric

1. Apr 18, 2013

### alexay95

i got sinx/siny=1.2

and i need to find cosx/cosy

can i do it or maybe i need more knowledge?

2. Apr 18, 2013

### Simon Bridge

Context perhaps?

3. Apr 18, 2013

### alexay95

its a problem at optics and i need to solve this problem.
that all i know from the problem given.

4. Apr 18, 2013

### Simon Bridge

It looks like you are trying to get an answer using an inefficient method.
What is the problem you are doing?

5. Apr 18, 2013

### HallsofIvy

For example, if sin(x) and sin(y) are both positive, cos(x) and cos(y) could be positive or negative. So for one value of sin(x)/sin(y) there are two different possible values for cos(x)/cos(y).

6. Apr 18, 2013

### alexay95

Why would it matter, u can say that sinx worth 0.5 and that's mean that cosx is positive and negative too.i just need a trigonometric connection between the two

7. Apr 18, 2013

### Simon Bridge

The general trig relationship between them is sin2θ + cos2θ = 1 because sinx and cosx are the opposite and adjacent sides of a right-angle triangle with unit hypotenuse.

if sinx=1/√2, then cosx=1/√2
But your problem is that you don't know what sinx is, what you know is the ratio of the sines of two angles ... sinx/siny.

In general: if sinx/siny=S, for a known S, then sinx and siny can take on any values that satisfy sinx=S.siny ... infinite possibilities. You need to know something about the relationship between x and y to narrow them down.

I do not understand your reluctance to share.