# cal3/algebra help me!

posted by
**Lucy**
.

Find and classify all local minima, local maxima, and saddle points of the function f(x,y)= -3yx^2-3xy^2+36xy

I really need help answering this one!! Please answer in detail! Thank you

This is what I have so far...

D=FxxFyy-(Fxy)^2=(-6y)(-6x)-(-6x-6y+36)^2

= 36xy-36(x+y-6)^2

Now set D=0 but I don't know how to solve it?? 36xy-36(x+y-6^2=0

Set Fx=0=-6x-6y+36 and set Fy=0=-6xy-3y^2+36y

I need help with the algebra, its been so long