1) 16x-12y=4(4x)+4(-3y)=4(4x-3y)
2) -10a^4-25a^9=-5a^4(2)-25a^9=-5a^4(2+5a^5)
3) x^5y-x^3y=x^3y(x^2)+x^3y(-1)=x^3y(x^2-1)=x^3y(x+1)(x-1)
4) 13a^2b-39a^3b^2+26abc= 13ab(a)+13ab(-3ba^2)+13ab(2c)=13ab(a-3ba^2+2c)=13ab(a-3a^b+2c)
5) 7x(a-b)-(4a-b)=7xa-7xb-(4a-b)=7xa-7xb-4a+b=7ax-7bx-4a+b
6) 2a(2x-y)+9(y-2x) = 4ax-2ay+9(y-2x)=4ax-2ay+9y-18x
7) 5(a-3b)-a(3b-a)= 5a-15b-a(3b-a)=5a-15b-3ab+a^2=(-5-a)(-a+3b)
8) (x-y)^2-5(x-y)=(x-y)((x-y))+(x-y)(-5)=(x-y)(x-y-5)