First, we need to expand the expression:

(х²-5х+2)(х²-5х-1)
= х²(х²) - 5х(х²) + 2(х²) - х²(5х) + 5х(5х) - 2(5х) - х²(-1) + 5х(-1) + 2(-1)
= х⁴ - 5х³ + 2х² - 5х³ + 25х² - 10х + х² - 5х - 2
= x⁴ - 10x³ + 28x² - 15x - 2

Since the expanded expression is equal to 28, we have:

х⁴ - 10х³ + 28х² - 15х - 2 = 28

And simplifying:

х⁴ - 10х³ + 28х² - 15х - 2 - 28 = 0
х⁴ - 10х³ + 28х² - 15х - 30 = 0

Therefore, the solution to the equation is x⁴ - 10x³ + 28x² - 15x - 30 = 0.