有2个数学题用简便做大哥大姐帮帮忙!
问题描述:
有2个数学题用简便做大哥大姐帮帮忙!
⑴1/(1*)+1/(5*7)+······+1/(1995*1997)+1/(1997*1999)
⑵1/(2*7)+1/(7*12)+1/(12*17)·····+1/(92*97)+1/(97+102)
答
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...