1x2+2x3+3x4+.99x100=?

来源：学生作业帮编辑：神马作文网作业帮分类：数学作业时间：2024/11/06 15:36:12

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+1)/6+n(n+1)/2
=n(n+1)[(2n+1)+3]/6
你令n=99,带入就可以了

1分之1x2+1分之2x3+1分之3x4.+1分之99x100 计算1x2+2x3+3x4+4x5+...+99x100 一定要帮我啊!(1/1x2)+(1/2x3)+(1/3x4)+(1/4x5)+.+(1/99x100)=? 1/1x2+1/2x3+1/3x4+1/4x5+.+1/98x99+1/99x100 1/1X2+1/2x3+1/3x4+1/4x5+.+1/98x99+1/99x100求结果! 2/1x2+2/2x3+2/3x4+2/4x5+...+2/98x99+2/99x100 求1x2,2x3,3x4,4x5,……98x99,99x100的倒数和 1x1-2x2+3x3-4x4+5x5-6x6.-100x100+101x101 1/(1x2)+1/(2x3)+1/(3x4)+．．．．．．+1/(99x100)=?要计算过程．简便计算1/2+1/2x3+1/3x4+1/4x5+...+1/99x100 1X2+2X4+3X6+.50X100 求线性方程组 x2-x3-x4=0 x1+x2-x3+3x4=1 x1-x2+x3+5x4=-1 x1+2x2-2x3+