已知函数f(x)=x^2/(x+m)的图像经过(4,8),数列{an}中,若a1=1,Sn为数列{an}的前n项和,an=f(Sn)(n≥2),证明数列{1/Sn}成等差数列,并求数列{an}的通项
问题描述:
已知函数f(x)=x^2/(x+m)的图像经过(4,8),数列{an}中,若a1=1,Sn为数列{an}的前n项和,an=f(Sn)(n≥2),证明数列{1/Sn}成等差数列,并求数列{an}的通项
答
f(4)=16/(4+m)=8m=-2an=Sn²/(Sn-2)Sn-S(n-1)=Sn²/(Sn-2)Sn²-2Sn-SnS(n-1)+2S(n-1)=Sn²2S(n-1)-2Sn=SnS(n-1)两边除2SnS(n-1)1/Sn-1/S(n-1)=1/2所以1/Sn等差1/Sn-1/S(n-1)=1/2d=1/21/S1=1/a1=1所...