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a(n+1)=2an/(an+1)
1/a(n+1) = (an+1)/(2an)
1/a(n+1) -1 = (1/2)( 1/an -1)
{1/an -1} 是等比数列,q=1/2
1/an -1 =( 1/2)^(n-1) .(1/a1 -1)
= -(1/2)^n
an = 1/[1-(1/2)^n] = 2^n/(2^n -1)
a1=1/2
a2 =1/(1-1/4) = 4/3
an 是递增数列,an>0
ie 0
1年前
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