（1）：12a^2-18ab^2-24a^3b^3
=6a(2a-3b²-4a²b³)
(2):5y^2-15y+5
=5(y²-3y+1)
(3):-27m^2 n+9mn^2-18mn
=-9mn(3m-n+2)
(4):6x(x-y)^2+3(y-x)
=3(x-y)(2x²-2xy-1)
(5):已知m-2n=8,mn=6,求代数式3m^2n-6mn^2+18n-9m的值.
3m^2n-6mn^2+18n-9m
=3mn(m-2n)-9(m-2n)
=(m-2n)(3mn-9)
=8(18-9)
=72