原式=1/2+2/3+……+99/100 =(1-1/2)+(1-1/3)+……(1-1/100) =100-(1/2+1/3+……+1/100) =100-（2*3*4*……*100）*99/2*3*4*……100 =100-99 =1
99/1001/1×2=1-1/2这样继续推最后只剩下1-1/100
