# Math Help - Differentiate two variables and find stationary point

1. ## Differentiate two variables and find stationary point

Question: Consider the function, f, of two variables defined by f(x,y) = (x^2 - 9)*sin(y). Find all the stationary points of f and classify each of them as either a local maximum, local minimum or a saddle point.

How would I answer this question?

2. ## Re: Differentiate two variables and find stationary point

At the stationary points $f_x=f_y=0$.

To classify them you need to consider $f_{xx}, f_{xy} \text{ and } f_{yy}$.

This is all in your notes presumably and it's quite routine.

There are some good videos out there and of course there's Wikipedia.