首页 > 留学知识库

问题: 已知数列a1=1,Sn=n^2*an,求an

已知数列a1=1,Sn=n^2*an,求an

解答:

n^2*an=Sn=S(n-1)+an=(n-1)^2*a(n-1)+an
=>an=an*n^2-(n-1)^2*a(n-1)
=>an/a(n-1)=n-1/n+1
=>an=(n-1)*(n-2)*...*1/(n+1)*n*...*3
=>an=2/(n*(n+1))