a(n+1)=2an/(an+2)1/a(n+1)=(an+2)/(2an)=1/an+1/21/a(n+1)-1/an=1/2,为定值.1/a1=1/1=1数列{1/an}是以1为首项,1/2为公差的等差数列.1/an=1/a1+(n-1)(1/2)=1+(n-1)/2=(n+1)/2an=2/(n+1)n=1时,a1=2/(1+1)=1,同样满足....