Ответ:

(x - 1)(5x + 4).

Объяснение:

5х² - х - 4

D = 1 + 80 = 81

x1 = (1 + 9)/(2•5) = 1;

x2 = (1 - 9)/(2•5) = - 8/10 = - 4/5;

5x² - x - 4 = 5•(x - 1)(x + 4/5) = (x - 1)(5x + 4).