# Thread: Brainfog on Identity

1. ## Brainfog on Identity

Hi
I have to make the bottom one from the top two and have simply forgot how to get there

2sinAcosA/cos^2A-Sin^2A

or alternatives of cos2A..but I am losing my way!

2. $\tan 2A=\frac{\sin 2A}{\cos 2A}=\frac{2\sin A\cos A}{\cos^2A-\sin^2A}=$

$=\frac{\dfrac{2\sin A\cos A}{\cos^2A}}{\dfrac{\cos^2A-\sin^2A}{\cos^2A}}=\frac{2\tan A}{1-\tan^2A}$

3. I knew I would kick myself
Many Thanks