Double angle (1 Viewer)

[nahi11]

Hi,

I deleted the previous since I doubt anyone was going to benefit from it. Could someone please what is happening here :

Thanks

 

[deswa1]

Do you know the t-substitutions? If you let t=tan(a/2), you'll find that sina=(2t)/(1+t^2) -> Then sub in tan(a/2) for t and the result follows

 

[nahi11]

oh lol thanks. I forgot.