Question

use the second derivative test to find local extrema and saddle point of f(x,y)=6x^2-2x^3+3y^2+6xy

Answer 1

df/dx=12x-6x^2+6y
df/dy=6y+6x
next step is to find critical points

Answer 2

set df/dy=0 and y=-x
i'm stuck on df/dx=0...

Answer 3

don't you need second derivative?

Answer 4

o wait, nevermind i use y=-x in setting df/dx=0 i think i can get it now (slapping forehead)