Sn=2n^2-3n
S(n-1)=2(n-1)^2-3(n-1)
想减得：An=4n-5
Bn=An*2^n=（4n-5）2^n
Tn=-2+3*2^2+……+(4n-5)2^n
2Tn= -2^2+……+(4n-9)2^n+(4n-5)2^(n+1)
想减得：Tn=（n+1)2^(n+3)-5*2^(n+1)-14
我的答案又对又快,求你了,亲.