来自童长忠的问题
1X2X3+2X3X4+.+n(n+1)(n+2)
1X2X3+2X3X4+.+n(n+1)(n+2)
1回答
2020-03-24 03:11
1X2X3+2X3X4+.+n(n+1)(n+2)
1X2X3+2X3X4+.+n(n+1)(n+2)
1*2*3+2*3*4+.+n*(n+1)(n+2)
=1/4[(1*2*3*4-0*1*2*3)+(2*3*4*5-1*2*3*4)+.+
n(n+1)(n+2)(n+3)-(n-1)n(n+1)(n+2)]
=1/4*n(n+1)(n+2)(n+3)