For the following geometric sequence find the recursive formula: {-1, 3, -9, }.

an = -3 · an - 1 where a1 = 1
an = -3 · an - 1 where a1 = -1
an = -1 · (-3)n - 1
an = (-3)n - 1

First term (a1) is -1

recursive formula goes like this

is the nth term
is the term before that

we normally have

we see each term is multipying by -3 to get next one

so that would be
where a1=-1

the 3rd option is correct except that it is the explicit formula

so answer is 2nd one