3.(1)6xy^2-4x^2y.
(2)-2mn-9m+3n
(3)-5a^2-8a+9b^3
(4)-ab+3
(5)-x^2y+xy-8x
(6)xy^2-9y^3
(7)2mn^2-4m-2
(8)-5a^2b
4(1)(-3/5)^5
(2)(a-b)^7
(3)-a^25
(4)1/64 x^6
(5)(a+b)^2
(6)-a^6b^3
(7)a^6
(8)1
(9)y^(n+1)
(10)a^2n
(11)a
(12)c^(4n)
7(1)x^2+ax+bx+ab
(2)9x^2-49y^2
(3)18x^2+78x+72
(4)(3/2)x^3y^2-6x^2y^2+3xy^3
(5)-5a^4b^5
(6)2a^2-3ab+6b^2
(7)a^3c
(8)m^2n^2-1
(9)9a+6b
(10)4x+5
给我最佳