# Math Help - Chain rule

1. ## Urgent help needed

Hi

I have this calculus question question which has caused me some trouble:

$z = y + f(x^2 - y^2)$

Where f is diffentiable

I need to show that

$y \frac{\partial z}{\partial x} + x \frac{\partial z}{\partial y} = x$

How do I show that?

Is it by using the chain rule ?

/Fred

2. Yes, use the chain rule. For example, partial d/dx of f(x^2-y^2) is f'(x^2-y^2) times partial d/dx of (x^2 - y^2). Here f' denotes the derivative of f as a function of a single variable.