3.1x2x3+2+3x4+…+n(n+1)(n+2)
问题描述:
3.1x2x3+2+3x4+…+n(n+1)(n+2)
答
1*2*3=(1*2*3*4-0*1*2*3)/42*3*4=(2*3*4*5-1*2*3*4)/43*4*5=(3*4*5*6-2*3*4*5)/4.n(n+1)(n+2)=[n*(n+1)*(n+2)*(n+3)-(n-1)*n*(n+1)*(n+2)]/4全部相加,前后抵消n(n+1)(n+2)=n*(n+1)*(n+2)*(n+3)/4