设等差数列{an}的前n项和为Sn,且a2n比an等于（4n-1）比（2n-1）,则S2n比Sn等于

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设等差数列{an}的前n项和为Sn,且a2n比an等于（4n-1）比（2n-1）,则S2n比Sn等于
设等差数列{an}的前n项和为Sn,且a2n比an等于（4n-1）比（2n-1）,则S2n比Sn等于

设等差数列{an}的前n项和为Sn,且a2n比an等于（4n-1）比（2n-1）,则S2n比Sn等于
A2n /An=(4n-1)/(2n-1)代入：A2n=A1+(2n-1)d,An=A1+(n-1)d,
可整理得：d＝2A1,代入下式
S2n/Sn=[2nA1+2n*(2n-1)*d/2]/[nA1+n*(n-1)*d/2]
=4

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