Answer
$a_n=2-3n$
Work Step by Step
We know that the general formula of an arithmetic sequence is given by $a_n=a_1+(n-1)d$
Here, we have $d=-3$
$a_n=a_1+(n-1)d$
This gives: $a_n=-1+(n-1) \times (-3)$
or, $a_n=-1-3n+3$
Hence, $a_n=2-3n$