Extrempunkte f'(x) = 0
3·x^2 - 2·a·x = x·(3·x - 2·a) = 0
x = 0
x = 2/3·a
f''(0) = -2·a
f''(2/3·a) = 2·a
f(0) = 0
f(2/3·a) = -4/27·a^3
Für a = 0 --> Sattelpunkt SP(0 | 0)
Für a > 0 --> HP(0 | 0) ; TP(2/3·a | -4/27·a^3)
Für a < 0 --> TP(0 | 0) ; HP(2/3·a | -4/27·a^3)