1X2X3+2X3X4+3X4+.+nx(n+1)(n+2)=

1/(1x2x3)+1/(2x3x4)+1/(3x4x5)+.1/(nx(n+1)x(n+2)=? 1x2x3+2x3x4+3x4x5+4x5x6+...+n(n+1)(n+2)= 求和1x2x3+2x3x4+...+n(n+1)(n+2) 1x2=(1/3)(1x2x3-0x1x2) 3x4=(1/3)(3x4x5-2x3x4) 问1x2x3+2x3x4+. 观察下列各式：1X2=1/3(1x2x3-0x1x2) 2x3=1/3(2x3x4-1x2x3) 3x4=1/3(3x4 1x2=1/3(1x2x3=0x1x2 ) 2x3=1/3(2x3x4-1x2x3) 3x4=1/3(3x4x5- 2x 1x2=1|3(1x2x3-0x1x2) 2x3=1|3(2x3x4-1x2x3) 3x4=1|3(3x4x5-2x3x 1x2=三分之一｛1x2x3-0x1x2｝；2x3-三分之一｛2x3x4-1x2x3｝：3x4-三分之一｛3x4x5-2 1x2X3+2x3X4+3x4X5+…+7X8X9=? 1x2x3+2x3x4+3x4x5+...+7x8x9=, 3.1x2x3+2+3x4+…+n(n+1)（n+2) 1/1x2x3+1/2x3x4+1/3x4x5