Originally Posted by

**ivanyo** edit - solved...haha i just realised you differentiate with respect to one first, then add the differential with respect to the other.

Hi everyone,

I just need some help on a question that I'm currently trying to solve. I'm doing Summer Maths at uni at the moment but I haven't quite grasped this concept.

The question is telling me to calculate a differential, given an equation.

*A = xy*

Find dA.

I know for a fact that the answer is dA = ydx + xdy, but I am unsure as to how the lecturer got to that process because he stated it was 'fairly self explanatory'. I guess I didn't have the guts to ask infront of a hundred people so here I am...haha

I don't expect a complete answer...moreso some guidance or references that will help me along the way.

Thanks in advanced,