That's what I thought as well to start with. I think the double angle formulas jump out at you.

But I thought the OP might not have met them so I looked to see if I could bypass them. The tan2A formula comes from dividing by cos so I tried that instead and nearly fell off my chair.

Good to offer a choice so not redundant.

Bob

]]>I still prefer the one-step method though, haha. So this post is a little redundant...

]]>Welcome to the forum!

I think you mean sin^2 (x) rather than sinx^2 ie.

Anyway start with the left hand side:

Divide top and bottom by

and it comes out straight away.

Bob

]]>(sinxcosx)/((cosx^2)-(sinx^2)) = ((tanx)/(1-tanx^2))

]]>