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知识梳理
双基自测
2.等差数列及其前n项和的性质 (1)若m+n=p+q,则 (m,n,p,q∈N*);m+n=2p,则am+an=2ap(m,n,p∈N*). (2)若{an}是等差数列,公差为d,则ak,ak+m,ak+2m,…(k,m∈N*)是公差为 的等差数列. (3)若{an},{bn}是等差数列,p,q∈R,则{pan+qbn}也是等差数列. (4)设Sn是等差数列{an}的前n项和,则数列 也是 数列. (5)若等差数列{an}的前n项和为Sn,则S2n-1=(2n-1)an. (6)若n为偶数,则 ;若n为奇数,则S奇-S偶=a中(中间项).
am+an=ap+aq
md
等差