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