Homework Statement
Determine the critical points f(x,y) = x^3y + xy
Homework Equations
The Attempt at a Solution
fx(x,y) = 3x^2 + y
3x^2y+y=0
y(3x^2 +1) = 0
y = 0
3x^2=1
x=1/3fy(x,y) = x^3 + x
x^3 + x = 0
x(x^2+1) = 0
x=0
x^2= -1
x= -1
I don't know how to take it from here as I have...