math prep108,求解，谢谢 看不明白

predy1

答案是C 可是我看不明白

108.
                11272-!-item-!-187;#058&007635

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

jesuiscjj

 tn - 1 - 3 打错了

n-1应该是下标

中学数学题

cjwbhu

Tn=T1-3(n-1)，代入Tn=-4,T1=23，求得n=10

predy1

感谢~感谢