Justify by geometric means that a linear utility function:

u(x) = ax + a2x2 +a3, a; > 0, i = 1, 2, 3 describes consumer goods which are perfect substitutes and not complementary for each other, and that a Koopmans-Leontief utility function: u(x) = min{ax1, a2x2} + az, aj > 0, i = 1, 2, 3 describes consumer goods which are perfect complements and not substitute for each other.