For each of the following, find the maximum and minimum of f on H.
a) f(x, y) = x2 + 2x - y2 and H = {(x, y) : x2 + 4y2 < 4}
b) f(x, y) = x2 + 2xy + 3y2, and H is the region bounded by the triangle with vertices (1,0), (1,2), (3,0)
c) f(x, y) = x3 + 3xy - y3, and H = [-1, 1] × [-1, 1]