等差数列{an},若公差d≠0,可以把通项看作是项数n的一次函数,即an=an+b(a≠0),因此通项反映的点对(n,an)一定分布在该函数所表示的直线上.同样,由等差数列前n项和Sn=an2+bn,得出Sn/n=an+b,因此Sn/n是关于n的一次函数,其反映的点对(n,Sn/n)也分布在该函数所表示的直线上.运用 Equal-difference sequence {an}, if the tolerance d ≠ 0, the general term can be regarded as a linear function of the number of items n, that is an = an + b (a ≠ 0), so the point pairs reflected by the general term (n, an ) must be distributed on the line represented by the function. Similarly, by the first n terms of the arithmetic progression and Sn=an2+bn, Sn/n=an+b is obtained, so Sn/n is a linear function of n, which The reflected pairs (n, Sn/n) are also distributed on the line represented by the function.