Two variable extreme value problem

[KaiserBrandon]

Homework Statement

alright so this is just a general question. In order to solve an extreme value problem, there's a part where I have to use f base xy. I'm not quite sure what that is, I know f base x is the partial derivative of the function with regards to x, and f base xx is the second partial derivative for x.

Homework Equations

none

The Attempt at a Solution

The only thing I can think of is that f base xy is simply the original function of x and y. Thanks in advance

 

[jakncoke]

F base xy means differentiate with x while keeping y constant, then take the rest and differentiate with respect to y keeping x constant.
example:
f(x,y)= 3x^2+2xy
f(x,y)x = 6x+2y
f(x,y)xy = 2

 

[KaiserBrandon]

ok you that makes sense. I guess I must have missed the class where we learned that lol. Thanks.