How do I write a recursive rule for the geometric series -5, -15, -45, -135?

Question

anonymous · Answer

$$-5,-5\times 3,-5\times 3^2,...$$

anonymous · Answer

i guess as a recursion you could say $a_1=-5,a_n=a_{n-1}\times 3$

marigirl · Answer

we can use the formula xn = ar^(n-1)
where a is the first term
r is the 'common ratio'

marigirl · Answer

as satellite73 pointed out
-5            -15                   -45              -135
     −5×3            −5×3^2        -5×3^3            (difference)

from that we can conclude the common ration r=3 ....

hope that makes sense. happy to clarify further

marigirl · Answer

what do u conclude as your geometrical seq rule for this?

anonymous · Answer

a(1) = -5
a(n+1) = 5 * a(n)

anonymous · Answer

i mean a(n+1) = 3 * a(n)

anonymous · Answer

I understand the common ratio and the first term but the n-1 is throwing me off, that's why I'm not sure how to write it, I already figured out the common ratio and the iterative rule for the sequence but I just don't get the recursive rule, none of this makes any sense to me at all.

anonymous · Answer

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anonymous · Answer

I don't go on IG.

anonymous · Answer

okay cool