Question

Picture with question help plz

Answer 1

Let $a_{1}$ = -9, $a_{2}$ = -12 and so on.

-15 = -9 + (-6)

-15 = -9 + 2(-3)

Let -3 be the common difference, or d.

$a_{n}$ = -9 + n(-3)

    = -9 - 3n