ax²+bx+c = a*(x-x1)(x-x2)
х²-х-30 = 0
D = (-1)²-4*1*(-30) = 1+120 = 121 = 11²
x1 = (1+11)/2*1 = 12/2 = 6
x2 = (1-11)/2*1 = -10/2 = -5
х²-х-30 = (x-6)(x+5)
