1) 9x*xy+8y*72= x(9+y)+8(y+9)=(x+8)(y+9)
2) bx*4b+ax*4a=b(x-4)+a(x-4)=(b+a)(x-4)
3)4a*ay+4b*by=a(4-y)+b(4-y)=(a+b)(4-y)
4)7ax*ay+7bx*by=a(7x-y)+b(7x-y)=(a+b)(7x-y)
5) 11ay*by-77a*7b=y(11a-b)-7(11a-b)=(y-7)(11a-b)
6)13x*ax+13y-ay=x(13-a)+y(13-a)=(x+y)(13-a)