根号[(1x2x3+2x4x6+...+nx2nx3n)/(1x3x4+2x6x8+...+nx3nx4n)）=?

根号[(1x2x3+2x4x6+...+nx2nx3n)/(1x3x4+2x6x8+...+nx3nx4n)）=? 1x2X3+2x3X4+3x4X5+…+7X8X9=? 1x2x3+2x3x4+3x4x5+...+7x8x9=, 1/1x2x3+1/2x3x4+1/3x4x5 求和1x2x3+2x3x4+...+n(n+1)(n+2) 1x2x3+2x3x4+3x4x5+…+8x9x10 1x2x3+2x3x4+3x4x5+.+10x11x12 1x2=(1/3)(1x2x3-0x1x2) 3x4=(1/3)(3x4x5-2x3x4) 问1x2x3+2x3x4+. 1/1x2x3+1/2x3x4+1/3x4x5+1/4x5x6+.+1/48x49x50= 1/1x2x3+1/2x3x4+1/3x4x5+.+1/11x12x13= 1/1x2x3+1/2x3x4+1/3x4x5+.+1/9x10x11= 请1/1x2x3+1/2x3x4+1/3x4x5+1/4x5x6=