Answer
$d=-10$.
$a_1= 74$,
$a_n= a_{n-1}-10$.
$a_n=84-10n$
Work Step by Step
1. Based on the given conditions, we have $a_8=a_1+7d=4$ and $a_{18}=a_1+17d=-96$, thus $10d=-100$ and $d=-10$.
2. We can find the first term $a_1=4-7(-10)=74$, and a recursive formula $a_n=a_{n-1}+d=a_{n-1}-10$.
3. We can find a formula for the nth term $a_n=a_1+(n-1)d=74+(n-1)(-10)=84-10n$
