I'm totally unsure of where to put this topic - sorry itll probably need moved.

Ok I'm doing a further maths A-level right now but I'm also doing an ordinary maths A-level at the same time. This causes a LOT of problems with my further maths, because I have not covered some of the topics in ordinary maths yet.

Anyway i'm having particular problems with Exact 1st order differential equations. It's probably something simple enough that im not getting but I dont understand how:

y + x(dy/dx) = x(cubed)

becomes

(d/dx)(xy) = x(cubed)

In my notes my teacher just wrote (y + x(dy/dx) is exactly the derivative of ?)

What is the question mark.

At the moment we are really rushing through the course, because i started the course late in the year, so doubtless I'll need more help from this forum.