1/11-11/31+2/11-12/31+3/11-13/31+.+10/1-20/31
=1/11x（1+10）x10÷2 -1/31x(11+20)x10÷2
=1/11x11x5-1/31x31x5
=5-5
=0
如果本题有什么不明白可以追问,