# Finding local extreme values

1. Mar 2, 2012

### bobsmith76

1. The problem statement, all variables and given/known data

see attachment

3. The attempt at a solution

I don't understand how they found fxy = 1

I understand how they found fxx, they used simultaneous equations, but I don't understand that notation.

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2. Mar 2, 2012

### LCKurtz

They didn't find $f_{xx}$ by using simultaneous equations. They just differentiated $f$ twice with respect to $x$. Then to get $f_{xy}$ they differentiated $f_x$ with respect to $y$.

3. Mar 2, 2012

### bobsmith76

Thanks, that makes sense.