Hello iihartheroSuppose . I assume that you've drawn a diagram. If so, you'll know that:

So

which can be re-written in terms of and (which is what we want!) as , using and (Can you do this bit?)

Similarly, using the other side of the diagram:

and

Now for the bit where you need to keep a clear head!

Using Pythagoras on

If you now multiply both sides by and divide by this will simplify to

, assuming

, again assuming

That wasn't so easy, was it?

Grandad