Question

等差数列3已知{an}是公差为d的等差数列,bn=1/n*(a1+a2+...an),数列{an}、{bn}的前n项和分

Answer 1

1=a1,b2=a1+d/2,b3=a2,...{bn}为首项是a1公差是d/2的等差数列.

Sn=1/2*n*(a1+a1+(n-1)d),Tn=1/2*n*(a1+a1+(n-1)d/2)

Sn-Tn=1/2*n*(n-1)d/2=1/4*d*n(n-1)

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