X^2 = 2x - 1 x^2 - 2x + 1 = 0 a = 1, b = -2, c = 1 D = b^2 - 4ac = 4 - 4*1*1 = 0. => есть 1 корень x1 = (-b + D) / 2a = (2+0)/2*1 = 1