1X2X3+2X3X4+.+n(n+1)(n+2)

3个回答

n(n+1)(n+2) = 1/4(n+3 - (n-1))*n(n+1)(n+2)
= 1/4n(n+1)(n+2)(n+3) - 1/4(n-1)(n)(n+1)(n+2)
所以，原式=1/4*[1*2*3*4 - 0 + 2*3*4*5 - 1*2*3*4 +...+
n(n+1)(n+2)(n+3) - (n-1)(n)(n+1)(n+2)]
=1/4n(n+1)(n+2)(n+3)

1x2x3+2x3x4+.+n(n+1)(n+2)=?
Sn=1/(1x2x3)+1/(2x3x4)+...+1/(n(n+1)(n+2))
1x2+2x3+3x4+.+n(n+1)=_____(n为自然数）
1x2x3+2x3x4+.+nx(n+1)(n+2)=?
1X2X3+2X3X4+...+n(n+1)(n+2)等于多少呢
求（1）lim2n^2-n+1/n2^+3n （2）limx^2+2x/x^2+4x+1 （3）lim(1/1+x-3/
x^n-1(3x^n+4x^n+1-5x^n+2)
1/1x2x3+1/2x3x4十……十1/n(n+1)(n十2)
因试分解(1)-2x^(5n-1)y^n+4x^(3n-1)y^(n+2)-2x^(n-1)y(n+4)(2)x^3-8
1）1x2+2x3+3x4+...+100x101= 2）1x2+2x3+3x4+...n(n+1)= （3）1x2x3