Can anyone explain...

[kid908]

Why you would use the determinate of the partial derivative of the gradient of function f at (a,b) to determine if that point is a local maxima or local minima?

D=|fxx fxy| = fxxfyy-(fxy)2
....|fyx fyy|

I understand the other condition of how fxx has to be greater than 0 to be a minima and fxx is less than 0 to be a maxima, but I don't understand why the determinate is used.

[Donut]

the forum does have a function for actual subscripts and super scripts. i dont even begin to know how to answer your question, but you dont have to use that [] thing for subscripts

[kid908]

Thanks, I found it.