1. The problem statement, all variables and given/known data Solve the differential equation. dy/dx = 4x + 4x/square root of (16-x^2) 2. Relevant equations Substituting using U... 3. The attempt at a solution I'm not sure if that's what I am supposed to do, but I tried using the U substitution... 4x + 4x/square root of (16-x^2) u = 16 - x^2 du = -2x -2du = 4x (I multiplied both sides by 2 and brought the negative over) -2 (integration sign [the S]) du + du/square root of u Take the anti-derivative... -2 x (u)^(-1/2) + C (changed square root into a power) -2 x (16-x^2) + C Unfortunately, that is not the answer they give me. I'm kinda stuck.. am I going in the right direction?