化简{[2*1d+3*2d+4*3d+……+n(n-1)d]+n(n-1)/2*d*a}/[(n-1)n*d/2]

问题描述:

化简{[2*1d+3*2d+4*3d+……+n(n-1)d]+n(n-1)/2*d*a}/[(n-1)n*d/2]

{[2*1d+3*2d+4*3d+……+n(n-1)d]+n(n-1)/2*d*a}/[(n-1)n*d/2] =[2*1d+3*2d+4*3d+……+n(n-1)d]/[(n-1)n*d/2] + n(n-1)/2*d*a/[(n-1)n*d/2] =2*[2*1+3*2+4*3+……+n(n-1)]/[(n-1)n]+a 下面求2*1+3*2+4*3+……+n(n-1)...