摘要
An arithmetic sequence is a sequence of numberseach of which,after the first,is obtained by addingto the preceding number a constant number calledthe common difference.Thus 3,7,11,15,19,…is an arithmeticsequence because each term is obtained by adding 4to the preceding number.In the arithmetic sequence50,45,40,…the common difference is 45-50=40-45=-5.General formulas for arithmetic sequencesinclude:the nth term an=a1+（n-1）d,and the sum of the first n
An arithmetic sequence is a sequence of numbers each of which, after the first, is obtained by adding to the preceding number a constant number called the common difference.
