2x^2 - 1/3*x - 1/3 = 0 | :2
x^2 - 1/6*x - 1/6 = 0 | +1/6
x^2 - 1/6*x = 1/6 | Quadratische Ergänzung
x^2 - 1/6*x + 1/12^2 = 1/6 + 1/12^2 | Binomische Formel
(x - 1/12)^2 = 25/144 | Wurzel
x - 1/12 = +- 5/12 | +1/12
x = 1/12 +- 5/12
x1 = 6/12 = 1/2
x2 = -4/12 = -1/3