knrt.net
当前位置:首页 >> 1x2+2x3+3x4+…+10x11=? >>

1x2+2x3+3x4+…+10x11=?

1x2+2x3+3x4+.+9x10+10x11 =10×11×12/6 =220

1x2+2x3+3x4+…+n(n+1) =1x(1+1)+2x(2+1)+3x(3+1)+…n(n+1) =(1^2+2^2+3^2+…+n^2)+(1+2+3+…+n) =n(n+1)(2n...

网站首页 | 网站地图
All rights reserved Powered by www.knrt.net
copyright ©right 2010-2021。
内容来自网络,如有侵犯请联系客服。zhit325@qq.com