原式=a^(2m-2)[a^(3n+2)+a^3nb^2-a^(n+2)-a^nb^2+b^2+a^2]
=a^(2m-2)[a^3n(a^2+b^2)-a^n(a^2+b^2)+(a^2+b^2)]
=a^(2m-2)(a^3n-a^n+1)(a^2+b^2)