Let f(x,y)=x4+y4−4xyf(x, y) = x^4 + y^4 - 4xyf(x,y)=x4+y4−4xy. Identify all local extrema of fff.
Local minimum at (1,1)(1, 1)(1,1)
Local minimum at (−1,−1)(-1, -1)(−1,−1)
Saddle point at (0,0)(0, 0)(0,0)
Local maximum at (0,0)(0, 0)(0,0)