1. The problem statement, all variables and given/known data Determine the critical points f(x,y) = x^3y + xy 2. Relevant equations 3. 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=1/3 fy(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 only seen this done where you substitute y values in equations for x. What are the critical points of the above? Thanks for the help!