1、原式=[2(a-1)+(b-1)][2(a-1)-(b-1)]
=(2a+b-3)(2a-b-1)
2、原式=(x^2y+xy^2)-(x+y)
=xy(x+y)-(x+y)
=(x+y)(xy-1)
3、原式=(a^2+b^2)^2-4(a^2+b^2)+4
=(a^2+b^2-2)^2ab-1+a-b(x+y)^2-2x-2y+1(m^2-2m)^2n+2n(m^2-2m)+na(2a-b)+2a(b-2a)^2-4(b-2a)^3客气