sn=(1/4)*(1/5)+(1/5)*(1/6)+.+(1/n+3)*(1/n+4)的值是多少

问题描述:

sn=(1/4)*(1/5)+(1/5)*(1/6)+.+(1/n+3)*(1/n+4)的值是多少

sn=(1/4)*(1/5)+(1/5)*(1/6)+.+(1/n+3)*(1/n+4)
=1/4-1/5+1/5-1/6+...+1/(n+3)-1/(n+4)
=1/4-1/(n+4)