问题
选择题
等差数列{an}，{bn}的前n项和分别为Sn，Tn，若
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答案
∵
=an bn
=2an 2bn
=a1+a2n-1 b1+b2n-1
=(2n-1)(a1+a2n-1) 2 (2n-1)(b1+b2n-1) 2 s2n-1 T2n-1
∴
=an bn
=2(2n-1) 3(2n-1)+1 2n-1 3n-1
故选B．
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等差数列{an}，{bn}的前n项和分别为Sn，Tn，若
|
∵
=an bn
=2an 2bn
=a1+a2n-1 b1+b2n-1
=(2n-1)(a1+a2n-1) 2 (2n-1)(b1+b2n-1) 2 s2n-1 T2n-1
∴
=an bn
=2(2n-1) 3(2n-1)+1 2n-1 3n-1
故选B．