1)=(х^3+6х^2)-(2х+12)=
=х^2(х+6)-2(х+6)=(х+6)(х^2-2)
2)=(-у^6-у^5)+(у^4+у^3)=
=-у^5(у+1)+у^3(у+1)=(у+1)(у^3-у^5)=
=у^3(у+1)(1-у^2)=
=у^3(у+1)(1-у)(1+у)=у^3(1-у)(у+1)^2
3)=х(2х^2+у^2)-у(2х^2+у^2)=
=(2х^2+у^2)(х-у)
4)=3а^2(2а-7б)+б^2(2а-7б)=
=(2а-7б)(3а^2+б^2)