Chapter 11 - Sequences; Induction; the Binomial Theorem - Section 11.2 Arithmetic Sequences - 11.2 Assess Your Understanding - Page 834: 36

$d=4$. $a_1= 48$, $a_n= a_{n-1}+4$. $a_n =4n+44$

1. Based on the given conditions, we have $a_{12}=a_1+11d=4$ and $a_{18}=a_1+17d=28$, thus $6d=24$ and $d=4$. 2. We can find the first term $a_1=4-11(4))=48$, and a recursive formula $a_n=a_{n-1}+d=a_{n-1}+4$. 3. We can find a formula for the nth term $a_n=a_1+(n-1)d=48+(n-1)(4)=4n+44$