分数裂项1/（1*5）+1/（3*5）+1/（5*7）+······+1/（1995*1997）+1/(1997*1999)＝(1/1-1/1999)*(1/2)=999/19991/（2*7）+1/(7*12）+1/（12*17）·····+1/（92*97）+1/（97+102）=(1/2-1/102)*(1/5)=5/51...