2020版高考数学(浙江专用)一轮总复习课件:6.2 等差数列
2020版高考数学(浙江专用)一轮总复习课件:6.2 等差数列第5页

d=0⇔{an}为常数列. (5)若{an}和{bn}均是等差数列,则{man+kbn}仍为等差数列,m,k为常数. (6)等差数列中依次k项的和成等差数列,即Sk,S2k-Sk,S3k-S2k,…成等差数列, 公差为k2d. (7)项数为偶数2n的非零等差数列{an},有 S2n=n(a1+a2n)=n(a2+a2n-1)=…=n(an+an+1)(an与an+1为中间的两项), S偶-S奇=nd, = . (8)项数为奇数2n-1的非零等差数列{an},有 S2n-1=⑤ (2n-1)an    (an为中间项), S奇-S偶=an, = .