3x²-28x+9=0

D= 784 - 4 * 9 * 3 =корень 676 = 26

x1= 28+26/6=9

x2= 28-26/6=0.33

По идее так

D = 784 - 4 (3 * 9) = 784 - 108 = 676

x1 = (28 - 26) / 6 = 2/6 = 1/3

x2 = (28 + 26) / 6 = 54/6 = 9

Ответ: 1/3 и 9