a1=2,(n+1)a(n+1)(角标)=nan,求an

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a1=2,(n+1)a(n+1)(角标)=nan,求an

a1=2,(n+1)a(n+1)(角标)=nan,求an
a1=2,(n+1)a(n+1)(角标)=nan,求an

a1=2,(n+1)a(n+1)(角标)=nan,求an
2a2=a1
3a3=2a2
4a4=3a3
.
nan=(n-1)an-1
等号两边相加,抵消,得到nan=a1,所以an=2/n

a_n = 2/n
解法是:a_n/a_n-1 = n-1/n;一项一项写,写到 a2/a1 = 1/2 ; 然后这一堆等式左右两边都乘起来,就有了

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