1) (18a²-27ab)+(14ac-21bc)=9a(2a-3b)+7c(2a-3b)=(2a-3b)(9a+7c);
3) 35ax+24xy-20ay-42x²=(35ax-20ay)+(24xy-42x²)=5a(7x-4y)-6x(7x-4y)=(7x-4y)(5a-6x).
1) xy²-by²-ax+ab+y²-a=(xy²-by²+y²)-(ax-ab+a)=y²(x-b+1)-a(x-b+1)=(x-b+1)(y²-a);
3) a²x²-bx²+a²x-bx+a²y-by=(a²x²+a²x+a²y)-(bx²+bx+by)=a²(x²+x+y)-b(x²+x+y)=(x²+x+y)(a-b²).