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Trigonometric Proof

Hi, please can I have some pointers proving this equation?

I know cos 2theta needs the double angle formula so either:

Cos^2 theta - sin^2 theta
2cos^2 theta - 1
1 - 2sin^2 theta

Then I know tan theta = sin theta / cos theta

And then sin 2 theta = 2 sin theta cos theta

Not sure where to use these, as using these Identities I either get 1 or 0 which is incorrect.

Original post by M.Johnson2111

This is one of those rare cases where, rather than starting with one side and seeing if it can be turned into the other, I would work on LHS - RHS. If you can show that this is zero, you have shown that LHS = RHS. You can do this using the identities you have already quoted - I would try and put everything in terms of theta rather than 2 theta.