# Trigonometric identity

1. May 3, 2007

### kasse

Which trigonometric identitiy are used to transform 2(cos(x))^2+2cos(x)sin(x) into 0?

2. May 3, 2007

### Curious3141

If you want to show that $$2\cos^2 x + 2\cos x \sin x = 0$$ identically, you can't because it isn't true.

If you want to solve the equation $$2\cos^2 x + 2\cos x \sin x = 0$$ that's a different matter entirely. So what is it you want to do?

3. May 3, 2007

### kasse

Sorry, I gave you the wrong eq. Solved in on my own here.

What's up in Singapore?

4. May 3, 2007

### Curious3141

Mostly the sky, I guess. :tongue2: