Identify the critical points of f(x,y)=x4+y4−4xyf(x, y) = x^4 + y^4 - 4xyf(x,y)=x4+y4−4xy.
(0,0),(1,1),(−1,−1)(0,0), (1,1), (-1,-1)(0,0),(1,1),(−1,−1)
(0,0),(1,1)(0,0), (1,1)(0,0),(1,1)
(1,1),(−1,−1)(1,1), (-1,-1)(1,1),(−1,−1)
(0,0),(1,1),(1,−1)(0,0), (1,1), (1,-1)(0,0),(1,1),(1,−1)