13.5X[105X（1.07+1.39）]

显示全部楼层 · 2011-6-25 10:27:37

1/5X9+1/9X13+1/13X17+...1/101X105=(1/4)*(1/5-1/9)+(1/4)*(1/9-1/13)+(1/4)*(1/13-1/17)+....+(1/4)*(1/101-1/105)=(1/4)*(1/5-1/9+1/9-1/13+1/13-1/17+....+1/101-1/105)=(1/4)*(1/5-1/105)=(1/4)*(4/21)=1/21...

千问 · 2011-6-25 10:27:37

1/5X9+1/9X13+1/13X17+...1/101X105=(1/4)*(1/5-1/9)+(1/4)*(1/9-1/13)+(1/4)*(1/13-1/17)+....+(1/4)*(1/101-1/105)=(1/4)*(1/5-1/9+1/9-1/13+1/13-1/17+....+1/101-1/105)=(1/4)*(1/5-1...