数列an的前n项和为Sn,a1=1,2Sn=a(n+1)-n^2/3-n-2/3
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数列an的前n项和为Sn,a1=1,2Sn=a(n+1)-n^2/3-n-2/3
(1)求通项
(2)求证1/a1+1/a2+3/a3+…+1/an
不好意思打错了,应该是2Sn/n=a(n+1)-n^2/3-n-2/3
(1)求通项
(2)求证1/a1+1/a2+3/a3+…+1/an
不好意思打错了,应该是2Sn/n=a(n+1)-n^2/3-n-2/3
![数列an的前n项和为Sn,a1=1,2Sn=a(n+1)-n^2/3-n-2/3](/uploads/image/z/19184943-39-3.jpg?t=%E6%95%B0%E5%88%97an%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn%2Ca1%3D1%2C2Sn%3Da%28n%2B1%29-n%5E2%2F3-n-2%2F3)
2Sn=na(n+1)-n^3/3-n^2-2n/3
2an=Sn-S(n-1)
an=n*a(n+1)/n+1-n
an/n=a(n+1)/n+1-1
1=a(n+1)/n+1-an/n
{an/n}成,首项为1,公差为1的等差数列
an/n=1+(n-1)=n
an=n^2
2an=Sn-S(n-1)
an=n*a(n+1)/n+1-n
an/n=a(n+1)/n+1-1
1=a(n+1)/n+1-an/n
{an/n}成,首项为1,公差为1的等差数列
an/n=1+(n-1)=n
an=n^2
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