M = 1/2·([-3, -7] + [5, 3]) = [1, -2]
MA = [-3, -7] - [1, -2] = [-4, -5]
A = [1, -2] + [-4, -5] = [-3, -7]
B = [1, -2] + [5, -4] = [6, -6]
C = [1, -2] + [4, 5] = [5, 3]
D = [1, -2] + [-5, 4] = [-4, 2]
~draw~ polygon(-3|-7 6|-6 5|3 -4|2);zoom(10) ~draw~