ПОМОГИТЕ!!!Заранее спасибо!!!

Решите задачу:

$7) \: \: 4a - ac - 4 + c = (4a - 4) - (ac - c) = 4(a - 1) - c(a - 1) = (a - 1)(4 - c)$
$8) \: \: {x}^{7} - {x}^{3} + 4 {x}^{4} - 4 = ( {x}^{7} - {x}^{3} ) + (4 {x}^{4} - 4) = {x}^{3} ( {x}^{4} - 1) + 4( {x}^{4} - 1) = ( {x}^{3} + 4)( {x}^{4} - 1) =( {x}^{3} + 4)( {x}^{2} - 1)( {x}^{2} + 1)$
$9) \: \: 6 {a}^{2} b - 3 {a}^{2} + 2ab - a = (6 {a}^{2} b - 3 {a}^{2} ) + (2ab - a) = 3 {a}^{2} (2b - 1) + a(2b - 1) = (3 {a}^{2} + a)(2b - 1) = a(3a + 1)(2b - 1)$