Chapter 11 - Sequences; Induction; the Binomial Theorem - Section 11.2 Arithmetic Sequences - 11.2 Assess Your Understanding - Page 834: 35

$d=-2$. $a_1= 25$, $a_n= a_{n-1}-2$. $a_n= 27-2n$

1. Based on the given conditions, we have $a_{14}=a_1+13d=-1$ and $a_{18}=a_1+17d=-9$, thus $4d=-8$ and $d=-2$. 2. We can find the first term $a_1=-1-13(-2)=25$, and a recursive formula $a_n=a_{n-1}+d=a_{n-1}-2$. 3. We can find a formula for the nth term $a_n=a_1+(n-1)d=25+(n-1)(-2)=27-2n$