1、|(11/12)-(12/13)|+|(12/13)-(13/14)|+|(13/14)-(14/15)|+|(14/15)-(15/16)|
=(1/12-1/13)+(1/13-1/14)+(1/14-1/15)+(1/15-1/16)
=1/12-1/16
=1/48
3、(1/2)+1+(1/2)=2,
(1/3)+(2/3)+1+(2/3)+(1/3)=3,
(1/4)+(2/4)+(3/4)+1+(3/4)+(2/4)+(3/4)=4,
1/n+2/n+...+(n-1)/n+1+(n-1)/n+(n-2)/n+...+1/n=n