1x2X3+2x3X4+3x4X5+…+7X8X9=?
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1x2X3+2x3X4+3x4X5+…+7X8X9=?1x2X3+2x3X4+3x4X5+…+7X8X9=?1x2X3+2x3X4+3x4X5+…+7X8X9=?一般的,有：(n-1)n(n+1)=n
1x2X3+2x3X4+3x4X5+…+7X8X9=?
1x2X3+2x3X4+3x4X5+…+7X8X9=?
1x2X3+2x3X4+3x4X5+…+7X8X9=?
一般的,有：
(n-1)n(n+1)
=n^3-n
{n^3}求和公式：Sn=[n(n+1)/2]^2
{n}求和公式：Sn=n(n+1)/2
1x2x3+2x3x4+3x4x5+.+7x8x9
=2^3-2+3^3-3+...+8^3-8
=(2^3+3^3+...+8^3)-(2+3+...+8)
=[(8*9/2)^2-1]-8*9/2+1
=1260
1x2x3+2x3x4+3x4x5+…+8x9x10
1x2X3+2x3X4+3x4X5+…+7X8X9=?
1x2x3+2x3x4+3x4x5+.+10x11x12
1x2x3+2x3x4+3x4x5+...+7x8x9=,
1x2x3 2x3x4 3x4x5 .10x11x12,怎么算
求和：1X2X3+2X3X4+3X4X5+...+98X99X100
1x2x3+2x3x4+3x4x5……+10x11x12巧算 请在两天之内回答
1/1x2x3+1/2x3x4+1/3x4x51/2x3x4 + 1/3x4x5 + 1/4x5x6 +……+1/99x100x101是 1/（2x3x4）
数学简便计算1/1x2x3+1/2x3x4+1/3x4x5……+1/20x21x22=?
1x2x3十2x3x4十3x4x5十…十7x8x9试着写出过程!
1x2=1|3(1x2x3-0x1x2) 2x3=1|3(2x3x4-1x2x3) 3x4=1|3(3x4x5-2x3x4)由此推断1x2x3+2x3x4+3x4x5.7x8x9=?
1x2=1/3x(1x2x3-0x1x2)2x3=1/3x(2x3x4-1x2x3)3x4=1/3x(3x4x5-2x3x4)求1x2x3+2x3x4+3x4x5+...+7x8x9=?
1/1x2x3+1/2x3x4+1/3x4x5+.+1/n(n+1)(n+2)
2/1x2x3+2/2x3x4+2/3x4x5+2/4x5x6+...+2/98x99x100=
1/1x2x3+1/2x3x4+1/3x4x5+.+1/8x9x10 求简算
请1/1x2x3+1/2x3x4+1/3x4x5+1/4x5x6=
1/1x2x3+1/2x3x4+1/3x4x5+------+1/98x99x100=
1/(1x2x3)+1/(2x3x4)+1/(3x4x5)+.1/(20x21x22)=?