f(x) = x * abs(x - 1)
f1(x) = x * (x - 1) = x^2 - x für x >= 1
F1(x) = 1/3·x^3 - 1/2·x^2
f2(x) = x * (-(x - 1)) = x * (-x + 1) = x * (1 - x) = x - x^2 für x <= 1
F2(x) = 1/2·x^2 - 1/3·x^3
∫ (-1 bis 2) f(x) dx = ∫ (-1 bis 1) f2(x) dx + ∫ (1 bis 2) f1(x) dx
F2(1) - F(-1) = 1/6 - 5/6 = -4/6 = -2/3
F1(2) - F1(1) = 2/3 - (- 1/6) = 5/6
-2/3 + 5/6 = 1/6