设N时最大
[（2/3)^(n+1)*(2(n+1)+0.5)]/（2/3)^n*(2n+0.5)
=2(2n+1.5)/[3(2n+0.5)]5/4
n=2时最大
（2/3)^n*(2n+0.5)
=（2/3)^2*(2*2+0.5)
=2十分感谢！但是第二步应该是=2(2n+2.5)/[3(2n+0.5)]<1n>7/4吧