由4a1=(a1+1)²得a1=1，由4an=4Sn-4S(n-1)整理得(an-1)²=(a(n-1)+1)²结合an为正项数列得等差数列an=2n-1则Tn=(1-1/3)+(1/3-1/5)+…<1Tn≥T1=2/3
