# Math Help - Need help finding a differential

1. ## Need help finding a differential

Find the differential of f(x,y)=z=xcos(xy)

2. ## Re: Need help finding a differential

I think you're looking for dz given that z is a function of x and y, so dz will be in terms of dx and dy. It's just the chain rule for two variables in a slightly different form:

$dz=\frac{\partial{z}}{\partial{x}}dx$ $+\frac{\partial{z}}{\partial{y}}dy$

Is that what you were looking for?

- Hollywood