Alright, I'm not technically stuck on this one, but I consistently get a result that disagrees with what Wolfram Alpha shows when I enter the problem to check my answer. Sorry 'bout the lack of LaTeX, but it should be simple enough to read. Here goes: Problem: Differentiate y=sin-1[x/(1+x)] Basically, I rearrange for sin(y)=x/(x+1) then use implicit differentiation to yield: * ---> cos(y)*(dy/(dx))=1/(x+1)2 Substituting with: cos(y)=sqrt[1-sin2(y)] I get: cos(y)=sqrt[1-x2/(x+1)2] which simplifies to: cos(y)=sqrt(2x+1)/(x+1) Dividing both sides of the original equation (above, marked with a star) by cos(y): dy/(dx)=1/[(x+1)sqrt(2x+1)] Which, if you don't like surds in the denominator, can be simplified to: sqrt(2x+1)/[(x+1)(2x+1)] I've done this question several times, and re-checked all my working. For the life of me, I can't see where I go wrong, yet my result is slightly different to what it should be. Any suggestions would be most welcome.