a^2(a-3)-(a-3)
=(a^2-1)(a-3)
=(a+1)(a-1)(a-3)
题目应是 2m(a-b)-3n(b-a)
=2m(a-b)+3n(a-b)
=(2m+3n)(a-b)
a^2-b^2-4a+4b
=a^2-4a+4-b^2+4b-4
=(a-2)^2-(b^2-4b+4)
=(a-2)^2-(b-2)^2
=(a-2+b-2)(a-2-b+2)
=(a+b-4)(a-b)
a^2(a-3)-(a-3)
=(a^2-1)(a-3)
=(a+1)(a-1)(a-3)
题目应是 2m(a-b)-3n(b-a)
=2m(a-b)+3n(a-b)
=(2m+3n)(a-b)
a^2-b^2-4a+4b
=a^2-4a+4-b^2+4b-4
=(a-2)^2-(b^2-4b+4)
=(a-2)^2-(b-2)^2
=(a-2+b-2)(a-2-b+2)
=(a+b-4)(a-b)