Suppose f is a function for which {(x, y): f(x, y) = 0 and f(x, y)=0} = {(1, 1), (1,-1), (-1,1),(-1,-1)}. Further supposes that for a=-1, a = 1 and b=-1, b = 1. faz(a, b)= ab, f(a, b)= ab, fa,(a, b) = a-b Which of the following points are local minimum? (1-1) (-1-1) (-1.1)