2/1+6/1+12/1+...+110/1 21/2+77/2+165/2+...+1677/2+2021/2

题目应该是分子分母都倒过来写了.
(1)原式=1/1*2+1/2*3+1/3*4+.+1/10*11
=(1/1-1/2)+(1/2-1/3)+(1/3-1/4).+(1/10-1/11)
=1-1/11=10/11
(2)原式=2/3*7+2/7*11+……+2/39*43+2/43*47
=(1/2)*(1/3-1/7)+(1/2)*(1/7-1/11)+……+(1/2)*(1/39-1/43)+(1/2)*(1/43-1/47)
=(1/2)*(1/3-1/7+1/7-1/11+……+1/39-1/43+1/43-1/47)
=(1/2)*(1/3-1/47)
=(1/2)*44/141=22/141 1+1/2+2/2+3/1+3/2+3/3+....+99/100+100/100呃、最后一题乐。1+1/2+2/2+1/3+2/3+3/3+....+99/100+100/100=2/2+3/2+4/2+5/2+.........+101/2=1/2*(2+3+4+....+101)=1/2*[(2+101)100/2]=103*25=2575