a(1)=3^1-2^1a(2)=3^2-2^2a(3)=3^3-2^3………………a(n)=3^n-2^n全部叠加：S(n)=(3^1+3^2+……+3^n)-(2^1+2^2+……+2^n)=[3(1-3^n)]/(1-3) - [2(1-2^n)]/(1-2)=[3^(n+1)-2^(n+2)+1]/2祝你学习天天向上~...