edit - solved...haha i just realised you differentiate with respect to one first, then add the differential with respect to the other.
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
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,
Suppose x and y are functions of some paramter, t: x= x(t), y= y(t). Then we can think of f(x,y) as a function of the single variable t.
By the chain rule, .
The differential, for a function of a single variable, is defined by so we have here
which is now independent of t.