\[4a^2 - 4ab - 5a + 5b = (4a^2 - 4ab) - (5a - 5b)\]
\[(4a^2 - 4ab) - (5a - 5b) = 4a(a - b) - 5(a - b)\]
\[4a(a - b) - 5(a - b) = (a - b)(4a - 5)\]
Ответ: (a - b)(4a - 5)