在数列{an}中,a1=2,an+1=an+ln(1+1⼀ n),则an=多少。

2025-06-28 09:22:17
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回答1:

由an+1=an+ln(1+1/n)
知an=a(n-1)+ln(1+1/n-1).
an=a(n-1)+ln(1+1/n-1)
an-1=a(n-2)+ln(1+1/n-2)
...
a2=a1+ln(1+1/1)
上述等式两边相加,得an=a1+ln(1+1/n-1)+ln(1+1/n-2)+...+ln(1+1/1)=2+ln(1+1/n-1)(1+1/n-2)...(1+1/1)=2+ln[n/(n-1)*(n-1)/(n-2)...2/1]=2+lnn