I still don't know the math symbols, so please bear with me!

I have the big S thing over sin(2X)*DX, its antidifferentiation is -(cos(2X))/2 + C

I have completely lost where that over 2 comes from. Wolfram alpha is not helpful. I realize that somewhere we pull a 1/2 out in front of everything, but I don't know where.

Thanks, I hope I'm making SOME sense.