a)
F(x, y) = (2·x^2 - 3·x·y)^2 - 81
f'(x) = - Fx / Fy = - (16·x^3 - 36·x^2·y + 18·x·y^2) / (18·x^2·y - 12·x^3) = 4/3 - y/x
b)
(2·3^2 - 3·3·y)^2 - 81 --> y = 3 ∨ y = 1
f'(3) = 4/3 - 3/3 = 1/3 an dem Punkt (3 | 3)
f'(3) = 4/3 - 1/3 = 1 an dem Punkt (3 | 1)