zinaidazina 1)
12a²b³-18a⁵b² = 6a²b²(2b-3a³);
2)
(b²-7)²-b(b²-7) = (b²-7)(b-7-b) = (b²-7)·(-7) = 7·(7-b²);
3)
8x+8y-ax-ay = 8(x+y)-a(x+y) = (x+y)(8-a); 
4)
8m⁷-6m²n-12m⁵n³+9n⁴ = (8m⁷-6m²n)-(12m⁵n³-9n⁴) =
= 2m²(4m⁵-3n)-3n³(4m⁵-3n) =
= (4m⁵-3n)(2m²-3n³).