It's been a while since I've done calculus and now a simple derivative is stumping me. This is the issue: d(xf)/dx= ? This is just the product rule, so I think: x(df/dx) + f (dx/dx)= x (df/dx) + f But I'm afraid that I don't even understand my own notation anymore (how embarrassing)... if I had a derivative like x (d/dx), would this just be the derivative of x, i.e. 1? So what does x df/dx mean? You can't simplify that anymore, right? Maybe I just need to go reread my calc 1 textbook..