1. The problem statement, all variables and given/known data Find dy / dx for sqrt(xy) = x - 2y. 2. Relevant equations I don't know how to simplify [(xy' + y) / 2sqrt(xy)] = (1 - 2y') to y' = [- y + 2sqrt(xy)] / [x + 4sqrt(xy)]. 3. The attempt at a solution I do everything Wolfram Alpha does here: http://www.wolframalpha.com/input/?i=derivative+sqrt(xy)+=+x+-+2y and at the end of the steps shown above, I want to multiply (1 - 2y') by 2sqrt(xy), to get 2sqrt(xy) - 4y'sqrt(xy) although I don't think that's correct. Help please. I just realized all I d is solve for y' (didn't occur to me for some reason), and now need to know if I plug in the original equation into all of the y values (I think I remember seeing my prof. do this in class). Ayuda me por favor.