In the arithmetic sequence t1, t2, t3, . . . , tn, . . . , t1 = 23
and tn = tn - 1 - 3 for each n > 1. What is the value of n when tn = -4 ?
(A) - 1
(B) 7
(C) 10
(D) 14
(E) 20
------------------------------------------------------------------------------------------------------------------------------------
【答案】 C
請問這題的思路是什麼
麻煩了
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 220.129.140.92