1x2+2x3+3x4+...+n(n+1)=?1x2x3+2x3x4+3x4x5+...+n(n+1)(n+2)=?

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1x2+2x3+3x4+...+n(n+1)=?1x2x3+2x3x4+3x4x5+...+n(n+1)(n+2)=?1x2+2x3+3x4+...+n(n+1)=?1x2x3+2x3x4+3x4x5

1x2+2x3+3x4+...+n(n+1)=?1x2x3+2x3x4+3x4x5+...+n(n+1)(n+2)=?
1x2+2x3+3x4+...+n(n+1)=?1x2x3+2x3x4+3x4x5+...+n(n+1)(n+2)=?

1x2+2x3+3x4+...+n(n+1)=?1x2x3+2x3x4+3x4x5+...+n(n+1)(n+2)=?
n(n+1)(n+2)/3
n(n+1)(n+2)(n+3)/4
.
定义：
n(n+1)(n+2)...(n+k)=[n]^k
则：
∑(i=1 to n)[n]^k=[n]^(k+1)/(k+1)=n(n+1)...(n+k+1)/(k+1)

（1*1+1）+（2*2+2）.......=（1*1+2*2+3*3......+N*N）+（1+2+3+4+...+N）=
同理，第二题乘出来：（1*1*1+2*2*2+3*3*3+......n*n*n）+3（1*1+2*2...+n*n）+2（1+2+3+4+..+n）=

数列求和

1X2+2X3+3X4+.NX(N+1) 1X2+2X3+3X4+.NX(N+1)规律 1x2+2x3+3x4+4x5+.+n(n+1)+n(n+2)=? 1x2+2x3+3x4...+10x11=?1x2+2x3+3x4...+nx(n-1)=? 1 1X2+2X3+3X4.n（n+1）（n+2）/ 1x2+2x3+3x4+.+n(n+1)=_____(n为自然数） 1/1X2+1/2X3+1/3X4+...+1/n(n+1)等于几? 1/1x2+1/2x3+1/3x4+...+1/n(n+1)怎么算计算:1/1x2+1/2x3+1/3x4+.+1/(n-1)n 求Sn=1/1x2+1/2x3+1/3x4+.+1/n(n+1) 1x2+2x3+3x4+4x5.n(n+1)等于多少?急救! 求使1x2+2x3+3x4+…+n(n+1) 1x2+2x3+3x4+...+n（n+1）=? 1/1X2+1/2X3+1/3X4+.+1/2010X2011=( ) 1/1X2+1/2X3+1/3X4+.+1/n(n+1)=( ) 1/1x2+1/2x3+1/3x4+...+1/nx(n+1)=_____ 1x2+2x3+3x4+...+nx(n+1)=只写结果 s=1x2+2x3+3x4+.nx(n+1）的和为多少求和：1X2+2X3+3X4+.+nX（n+1）?