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

Question

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## Answers ( )

Based on these first few terms, we can deduce that the next term is computed by switching the sign of the previous one, and multiplying it by 3: we start with -1, we switch the sign (1) and multiply by 3 (3); then again we switch the sign (-3) and multiply by 3 (-9), and so on.

Since switching sign is the same as multiplying by -1, we can compute every next term by multiplying the previous one by -3:

So, the recursive formula is

because it states precisely that the next term is -3 times the previous one.