# Trig problem

1. Jul 19, 2004

### VantagePoint72

Hey everyone,
I'm trying to solve for theta in a derivitive of a ballistics equation and I'm afraid I'm stuck. My trigonometry is a little rusty, can someone help me out? I have:

cos(theta)*sin(theta)=gd/2v^2

With the information I'm given I can solve the the right side of the equation ending up with:

cos(theta)*sin(theta)=some number

How do I get theta by knowing what cos(theta)*sin(theta) equals?

Thanks!

2. Jul 19, 2004

### Muzza

cos(t)sin(t) = 2sin(t)cos(t)/2 = sin(2t)/2. Now you can use arcsine...

3. Jul 19, 2004

### Gokul43201

Staff Emeritus
Just clarifying what Muzza wrote above...so there's no room for misunderstanding :

$$cos(t)sin(t) = \frac {2sin(t)cos(t)}{2} = \frac {sin(2t)}{2}.$$

4. Jul 19, 2004

### VantagePoint72

OK, thanks for the help!