1/3-1/4+……+1/(2n+1)-1/(2n+2)=1/3*4+1/5*6+1/7*8+。。。+1/[（2n+1）（2n+2）]<1/12+1/4*6+1/6*8+...+1/2n(2n+2)<1/12+1/2*(1/4-1/6+1/6-1/8+...+1/2n-1/(2n+2))=1/12+1/2*(1/4-1/(2n+2))<1/12+1/8=5/24<7/24
