9x^2 - 13x + 4 = 0;
D = b^2 - 4ac = (-13)^2 - 4 * 9 * 4 = 169 - 144 = 25;
x1 = (-b + √D)/2a = (13 + √25)/2 * 9 = (13 + 5)/18 = 18/18 = 1;
x2 = (-b - √D)/2a = (13 - √25)/2 * 9 = (13 - 5)/18 = 8/18 = 4/9.
9x^2 - 13x + 4 = 0;
D = b^2 - 4ac = (-13)^2 - 4 * 9 * 4 = 169 - 144 = 25;
x1 = (-b + √D)/2a = (13 + √25)/2 * 9 = (13 + 5)/18 = 18/18 = 1;
x2 = (-b - √D)/2a = (13 - √25)/2 * 9 = (13 - 5)/18 = 8/18 = 4/9.