How do i evaluate

It is part of a previous question where i prooved that the derivative of

I'm sure that i have to do some rearranging of the problem to get it into the derivative of [tex] sech^-1(x) [\math].

I have tried to do the problem and so far the solution i have is

Either i have made a mistake somewhere or i am going about the problem the wrong way but i have hit a brick wall. Can someone please give me some feedback on what i need to do or what i have done wrong