x^2 + x - 6 = 0;

D = b^2 + 4ac = 1^2 - 4 * 1 * (-6) = 1 + 24 = 25;

x1 = (-b + √D)/2a = (-1 + 5)/2 = 4/2 = 2;

x2 = (-b - √D)/2 = (-1 - 5)/2 = -6/2 = -3;

ax^2 + bx + c = a(x - x1)(x - x2);

x^2 + x - 6 = (x + 3)(x - 2).