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知识梳理
双击自测
3.等差数列及其前n项和的性质 (1)若{an}为等差数列,m+n=p+q,则am+an=ap+aq (m,n,p,q∈N*). 特别地,当m+n=2p,则am+an=2ap . (2)若{an}是等差数列,公差为d,则ak,ak+m,ak+2m,…(k,m∈N*)是等差 数列. (3)若Sn是等差数列{an}的前n项和,则数列Sm,S2m-Sm,S3m-S2m,…也是等差 数列. (4)若{an},{bn}是等差数列,则{pan+qbn}也是等差 数列.
