1X2X3+2X3X4+...+n(n+1)(n+2)等于多少呢
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1X2X3+2X3X4+...+n(n+1)(n+2)等于多少呢
![1X2X3+2X3X4+...+n(n+1)(n+2)等于多少呢](/uploads/image/z/19824411-3-1.jpg?t=1X2X3%2B2X3X4%2B...%2Bn%28n%2B1%29%28n%2B2%29%E7%AD%89%E4%BA%8E%E5%A4%9A%E5%B0%91%E5%91%A2)
由1×2×3+2×3×4+.+n(n+1)(n+2)=n(n+1)(n+2)(n+3)/4.
再问: 为啥呢。
再答: 你如果有兴趣,自己可以在网上看。 由1×2×3+2×3×4+3×4×5+。。。+n(n+1)(n+2) =(1/4)[1×2×3×4+2×3×4×4+3×4×5×4+。。。+n(n+1)(n+2)×4] =(1/4)[1×2×3×4+2×3×4×(5-1)+3×4×5×(6-2)+。。。+n(n+1)(n+2)×[(n+3-(n-1)]] =(1/4)[1×2×3×4+(2×3×4×5-1×2×3×4)+(3×4×5×6-2×3×4×5)+。。。(n(n+1)(n+2)(n+3)-(n-1)n(n+1)(n+2)] =(1/4)n(n+1)(n+2)(n+3) 前面的项相消,剩下最后面一项。
再问: 为啥呢。
再答: 你如果有兴趣,自己可以在网上看。 由1×2×3+2×3×4+3×4×5+。。。+n(n+1)(n+2) =(1/4)[1×2×3×4+2×3×4×4+3×4×5×4+。。。+n(n+1)(n+2)×4] =(1/4)[1×2×3×4+2×3×4×(5-1)+3×4×5×(6-2)+。。。+n(n+1)(n+2)×[(n+3-(n-1)]] =(1/4)[1×2×3×4+(2×3×4×5-1×2×3×4)+(3×4×5×6-2×3×4×5)+。。。(n(n+1)(n+2)(n+3)-(n-1)n(n+1)(n+2)] =(1/4)n(n+1)(n+2)(n+3) 前面的项相消,剩下最后面一项。
求和1x2x3+2x3x4+...+n(n+1)(n+2)
1x2x3+2x3x4+3x4x5+4x5x6+...+n(n+1)(n+2)=
1/(1x2x3)+1/(2x3x4)+1/(3x4x5)+.1/(nx(n+1)x(n+2)=?
急,裂项法计算1.1/1x2x3+1/2x3x4+…+1/n(n+1)(n+2)2.2/(X+2)(X+4)+2/(X+
n(n+1)(n+2)等于多少?
1/1x2x3+1/2x3x4+1/3x4x5+1/4x5x6+...+1/8x9x10 等于多少?
3.1x2x3+2+3x4+…+n(n+1)(n+2)
1/1x2x3+1/2x3x4+1/3x4x5
1x2X3+2x3X4+3x4X5+…+7X8X9=?
1x2x3+2x3x4+3x4x5+…+8x9x10
1x2x3+2x3x4+3x4x5+...+7x8x9=,
1x2x3+2x3x4+3x4x5+.+10x11x12