D = 81 - 4*14=25
x1 = (9-5)/2= 2
x2 = (9+5)/2 = 7
x2 - x1 = 7 - 2 = 5

x^2 - 9x + 14 = 0

D = V(81 - 4*14) = 5

x = (9 +/-  5) /2

x1 = 7           x2 = 2

Разность между ними

7 - 2 = 5