题目

3,5,-5,…
The first term in the sequence of numbers shown above is 3.Each even-numbered term is 2 more than the previous term and each odd-numbered term,after the first,is -1 times the previous term.For example,the second term is 3+2,and the third term is (-1)*5.What is the 55th term of the sequence?
A.-5 B.-3 C.-1 D.3 E.5
这道题目我不是很看得懂.额.Each even-numbered term is 2 more than the previous term这句
这题来自SAT OG P398 Q13

提问时间：2020-10-25

答案

同学,这道题实际上是非常简单滴...因为你接着写下去,所有数字依次是3,5,-5,-3,3,5,-5,-3,3.发现3,5,-5,-3形成了一个循环...55除以4,等于13余3,所以就是-5啦
Each even-numbered term is 2 more than the previous term意思就是每个偶数项都比前面的数大2,比如,5是第二项,是偶数项,所以他比3大2,-5是奇数项,所以他是前面的数,也就是5的-1倍,明白?