归纳推理：an为等差数列且bn=(a1+2a2+...+nan)/(1+2+3+...+n) 则bn为等差数列那么cn为等比数列dn=?

首先探究已知：bn={a1+2(a1+d)+3(a1+2d)+.+n(a1+(n-1)d)}/(1+2+3+4+.+n) =a1+AA=d∑(i^2-i)/∑i=d{n(n+1)(2n+1)/6 - n(n+1)/2}/{n(n+1)/2}=2(n-1)d/3即bn为以a1为起始项,2d/3为公差的等差数列.由此...