(a-4)(a-3)
(4a-1)(2-3a)
(5m-2n)(3n-5m)
(-2a-3b)(-3a+4b)

(a - 4)(a - 3) = а² - 3a - 4a + 12 = a² - 7a + 12 (4a - 1)(2 - 3a) = 8a - 12a² - 2 + 3a = -12a² + 11a - 2 (5m - 2n)(3n - 5m) = 15mn - 25m² - 6n² + 10mn = -25m² + 25mn - 6n² (-2a - 3b)(-3a + 4b) = 6a² - 8ab + 9ab - 12b² = 6a² + ab - 12b²