There should be three points I believeI found these ones alr

There should be three points I believe...I found these ones already: (4,0),(0,sqrt(2))

Solution

df/dx (partial derivatives) = 8-2x - 4y^2 df/dy= -4x * 2y= -8xy df/df =0 => x=0 or y=0 let x=0 then 8-2*0- 4y^2 =0 => y^2= 2 => y= sqrt(2) or -sqrt(2) y=0 => 8-2x=0 => x=4 so the critical points are (4,0),(0,sqrt(2)), (0, -sqrt(2))`