记Cn=an×bn,求数列{Cn}的前n项和Tn,在线等!an=4n-11bn=2^n-1
问题描述：
记Cn=an×bn,求数列{Cn}的前n项和Tn,在线等!
an=4n-11
bn=2^n-1
答
Cn=(4n-11)(2^n-1)=(4n-11)2^n-4n+11
令Sn=(4n-11)2^n=-7*2-3*2^2+2^3``````+(4n-11)2^n
则2Sn=(4n-11)2^(n+1)=-7*2^2``````````
2Sn-Sn=``````
即求出Cn
最后求Tn