Answer
$a_n=a_1+(n-1)d$;
$\text{first term}$;
$\text{common difference}$
Work Step by Step
Recall:
In an arithmetic sequences, the $n^{\text{th}}$ term is given by the formula:
$$a_n=a_1+(n-1)d$$
where
$d$=common difference
$a_1$=first term
Thus, the missing expressions in the given statements (in order) are:
$a_n=a_1+(n-1)(d$;
$\text{first term}$;
$\text{common difference}$
