Following toggle tip provides clarification

# Partial Differentiation (Metric)

Learn, or revise, the principles and techniques of partial differentiation.

## Units

### Principles

The partial derivatve, the chain rule and higher derivatives.

The partial derivatives $$\partial z/\partial x$$ and $$\partial z/\partial y$$.

The Chain Rule for partial derivatives; change of variable.

The higher derivatives $$\partial^2z/\partial x^2$$, $$\partial^2z/\partial x\partial y$$, etc.

### Techniques

Finding and classifying stationary points on surfaces.

Finding stationary points on surfaces by solving $$\partial z/\partial x = \partial z/\partial y = 0$$.

Classifying stationary points by considering $$z_{xx}\,z_{yy}-{z_{xy}}^2$$.