等差数列{an}的前n项和Sn=n^2+3n 则此数列的公差d?求详解

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等差数列{an}的前n项和Sn=n^2+3n则此数列的公差d?求详解等差数列{an}的前n项和Sn=n^2+3n则此数列的公差d?求详解等差数列{an}的前n项和Sn=n^2+3n则此数列的公差d?求

等差数列{an}的前n项和Sn=n^2+3n 则此数列的公差d?求详解
等差数列{an}的前n项和Sn=n^2+3n 则此数列的公差d?求详解

等差数列{an}的前n项和Sn=n^2+3n 则此数列的公差d?求详解
an=Sn-S(n-1)
=n²+3n-(n-1)²-3(n-1)
=2n+4
所以d=a(n+1)-an
=(2n+6)-(2n+4)
=2

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