Tn
=1 - 1/2 + (1/3 - 1/4) + (1/5 - 1/6) ....
=1/1*2 + 1/3*4 + +1/5*6 + .... + 1/(2n-1)*2n
=37/60 + 1/7*8 + ... + 1/(2n-1)*2n
=37/60 + A
然后证明A<根号2/2 - 37/60:
2A< 1/6*7 + 1/8*9 + ... + 1/(2n-2)(2n-1) + 1/7*8 + ... + 1/(2n-1)*2n = 1/6- 1/2n <1/6
即A<1/12<根号2/2 - 37/60