[SOLVED] Prove the identity, Stuck?

Hi, I tried doing this equation over and over, but I can't seem to get it! I've had sleepless nights for the past week...lol. So, please help me and put me out of my misery, I beg you...

I need to prove that:

this is what I came up with so far on the LHS, using :

And that's where I got stuck. I don't even think my working out is right...

PS. I tried using Wolfram|Alpha to solve it but it just tells me that the equation is true and gives me alternate forms, it doesn't show me steps which I need in order to fully understand, ya know?