等差数列an中,a(n+1)=2n+1,则Sn=(1/a1a2)+（1/a2a3）…（1/a99a100）=
人气：127 ℃ 时间：2020-04-15 01:19:15
解答
a(n+1)=2(n+1)-1所以an=2n-1所以 Sn=1/1*3+1/3*5+……+1/197*199=(1/2)(1-1/3)+(1/2)(1/3-1/5)+……+(1/2)(1/197-1/199)=(1/2)(1-1/3+1/3-1/5+……+1/197-1/199)=(1/2)(1-1/199)=99/199
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