Answer
$a_n=-3(-2)^{n-1}$
$a_4=24$
Work Step by Step
We are given:
$a=-3, r=-2$
We know that a geometric sequence has the form:
$a_{n}=ar^{n-1}$
Thus:
$a_n=-3(-2)^{n-1}$
So:
$a_4=-3(-2)^{3}=24$
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