Find the absolute minimum value of the function (f(x, y) = 2xy - 4x - 2y) over the closed triangular region (D) having vertices P(1, 0), Q(1, 5), R(6, 0).
a) (f(1, 0))
b) (f(1, 5))
c) (f(6, 0))
d) Depends on the shape of (D)