Answer
$A_{n}=(-1/3)^n$
Work Step by Step
Each term is successively being multiplied by -1/3 with the first term in fact being -1/3. Thus we can say the sequence with common ratio -1/3 is$A_{n}=(-1/3)^n$. Also acceptable is$A_{n}=(1/3)^n\times(-1)^{n}$
