# Math Help - Proving trig equation

1. ## Proving trig equation

I'm having trouble proving trig identities. Especially when the answers don't seem too obvious (you know, cancel something out here, cancel something out there, and then there's the answer). Here's the question I'm stuck on:

$\frac{\sin2\theta}{2-2\cos^2\theta}$= $\cot\theta$

If anyone can help, that would be appreciated!

2. $\frac{\sin2\theta}{2-2\cos^2\theta}$= $\cot\theta$

In this equation, try replacing $\sin2\theta$ with its identity = $2\sin\theta\cos\theta$
In the denominator, try factoring out the 2 and seeing what the equation could be equal to.
Recall $\sin^2\theta + \cos^2\theta = 1$

3. Originally Posted by cuteangel
$\frac{\sin2\theta}{2-2\cos^2\theta}$= $\cot\theta$

In this equation, try replacing $\sin2\theta$ with its identity = $2\sin\theta\cos\theta$
In the denominator, try factoring out the 2 and seeing what the equation could be equal to.
Recall $\sin^2\theta + \cos^2\theta = 1$
So I get $2-2\sin^2\theta$ on the bottom?

4. Well, not exactly.
$2 - 2\cos^2\theta = 2(1 - cos^2\theta)$
Now, rearranging $\sin^2\theta + \cos^2\theta = 1$ gives
$1 - \cos^2\theta = \sin^2\theta$
If you substitute this value in now, the equation should be solvable.

5. Can you take out a common factor in the denominator? Can it be simplified using the Pythagorean Identity?