Write the recursive formula for the geometric sequence. A^1=-2 A^2=8 A^3=-32

Question

anonymous · Answer

and its not An=-2*an-1

anonymous · Answer

well the first thing i see is it alternates between positive and negative.  do you know how to write that?

anonymous · Answer

no

anonymous · Answer

$$\huge (-1)^n$$

do you see how we would jump back and forth between -1 and 1?

anonymous · Answer

yes

anonymous · Answer

but on all of my answers it stays -1

anonymous · Answer

Great! now all we need to figure out is how it goes from 2, 8 and then 32.

anonymous · Answer

alright

anonymous · Answer

Is this a multiple choice question or do you have an answer booklet of some sort?

anonymous · Answer

I could be misunderstanding the question. :/

anonymous · Answer

A. an=-4+an-1
B. an=-2+an-1
D. an=-4*an-1

anonymous · Answer

th reason i didnt write c is because its the wrong answer

anonymous · Answer

Ah, i see what we need to do here. http://www.algebralab.org/lessons/lesson.aspx?file=algebra_geoseq.xml We need to find the common ratio and then we'll have our answer. It talks about that in the first paragraph or so on that website.

anonymous · Answer

so we just need to know what we can multiply the first term by that gives us 8 and then that number has to work when multiplying it by 8 to get 32.

Does that make sense?

anonymous · Answer

yea

anonymous · Answer

So basically that pattern i was talking about before.  Just ignore my (-1)^n stuff.  That's for a different representation okay?

anonymous · Answer

So you can setup an equation to figure it out. :D
$$\huge -2*x=8$$$$\huge 8*x=-32$$
x must be the same number for both answer.  give it a try.

anonymous · Answer

Once you find x, your answer will be in the form:
$$\huge a_n=a_{n-1}*x$$
I hope that all makes sense! :D