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1/（n+1）+1/（n+2）+...1/2n条件没给全，原题是Sn=1/（n+1）+1/（n+2）+...1/2n,求Sn-1
题目详情
1/（n+1）+1/（n+2）+...1/2n
条件没给全，原题是 Sn=1/（n+1）+1/（n+2）+...1/2n,求Sn-1
条件没给全，原题是 Sn=1/（n+1）+1/（n+2）+...1/2n,求Sn-1
▼优质解答
答案和解析
S(n-1)=1/n+1/(n+1)+……+1/2(n-1)=1/n+[1/(n+1)+1/(n+2)+……+1/2n]-1/(2n-1)-1/2n
=1/n-1/(2n-1)-1/2n+Sn
=-1/[2n(2n-1)]+Sn
=1/n-1/(2n-1)-1/2n+Sn
=-1/[2n(2n-1)]+Sn
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