分解因式（1）3a^3+12a^2b+12ab^2 (2) -6m^3n^2-3m^2n^2+12m^2n^3 (3) 2a^2b^2-28ab+98 (4) 6a^2-a^3-9a

（1）3a^3+12a^2b+12ab^2
=3a(a^2+4ab+4b^2)
=3a(a+2b)^2
(2) -6m^3n^2-3m^2n^2+12m^2n^3
=-3m^2n^2(2m+1-4n)
(3) 2a^2b^2-28ab+98
=2(a^2b^2-14ab+49)
=2(ab-7)^2
(4) 6a^2-a^3-9a
=-a(a^2-6a+9)
=-a(a-3)^2