1x2x3+2x3x4+3x4x5+.+n(n+1)(n+2)等于多少.1X2+2X3+3X4+....+n(n+1)=1/3Xn(n+1)(n+2)

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1x2x3+2x3x4+3x4x5+.+n(n+1)(n+2)等于多少.1X2+2X3+3X4+....+n(n+1)=1/3Xn(n+1)(n+2)1x2x3+2x3x4+3x4x5+.+n(n+1

1x2x3+2x3x4+3x4x5+.+n(n+1)(n+2)等于多少.1X2+2X3+3X4+....+n(n+1)=1/3Xn(n+1)(n+2)
1x2x3+2x3x4+3x4x5+.+n(n+1)(n+2)
等于多少.
1X2+2X3+3X4+....+n(n+1)=1/3Xn(n+1)(n+2)

1x2x3+2x3x4+3x4x5+.+n(n+1)(n+2)等于多少.1X2+2X3+3X4+....+n(n+1)=1/3Xn(n+1)(n+2)
1+2+...+n=n(n+1)/2
1^2+2^2+…+n^2=n(n+1)(2n+1)/6
1^3+2^3+…+n^3=n^2 * (n+1)^2 / 4
明确这三个式子就好了.

代入式子成立加设当n=k时代入式子是否成立（肯定是成立的）所以当N=K+1时代入式子就成立所以此题得证归纳法好麻烦的就不给你步骤了 ①

1/4*n*(n+1)(n+2)(n+3)

1x2x3+2x3x4+3x4x5+…+8x9x10 1x2x3+2x3x4+3x4x5+.+10x11x12 1x2x3+2x3x4+3x4x5+...+7x8x9=, 1x2X3+2x3X4+3x4X5+…+7X8X9=? 1x2x3 2x3x4 3x4x5 .10x11x12,怎么算求和：1X2X3+2X3X4+3X4X5+...+98X99X100 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)=? 1/1x2x3+1/2x3x4+1/3x4x5+.+1/9x10x11= 1/1x2x3+1/2x3x4+1/3x4x5+.1/98x99x100=要有中间过程 1/1x2x3+1/2x3x4+1/3x4x5+.+1/11x12x13= 1x2x3+2x3x4+3x4x5+4x5x6+...+n(n+1)(n+2)=