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Re: Geometric Sequences and Series

Subject: Re: Geometric Sequences and Series
From: JEMebius
Date: Sun, 30 Apr 2006 11:47:50 +0100
Newsgroups: sci.math
Simplest solution for this specific problem:

(A)
Make the assumption that you have to do with a geometric sequence.

Stricly speaking, the evidence for this is flimsy; it is based on the look of three terms and two ratios. The two ratios happen to be equal.

If you would assume that you have to do with an arithmetic sequence: no!, except if c=1 - since only for c=1 the two differences you have at your disposal are equal. But for c=1 the problem is no longer there.

In general the three terms given define a second-order arithmetic sequence. This is no common classroom stuff, I guess.

This is an example of the usual well-known situation in classroom and intelligence test problems.
BTW, I like much to play schoolmaster and beyond once in a while.

(B)
Just write down the first ten terms: the exponents are -4, -2, 0, 2, 4, 6, 8, 10, 12, 14.

Cheers: Johan E. Mebius


Shaynelle@xxxxxxxxx wrote:

I'm having a bit of trouble with solving this sequence:  (I need to
supply the tenth term)

(I'm putting extra spaces in between because I find it difficult to
read otherwise)


c ^ - 4, -c ^ - 2, 1...


the difference appears to be - c ^ -2 - correct?  If so, when I try and

solve for the tenth term, I have the following:


term 10 = term1 + (n-1) d
= c ^ - 4 + (9) (- c ^ - 2)
= c ^ - 4 + (- 9 c ^ - 2)
= c ^ - 4 - 9 c ^ - 2


Do I have this correct so far?  If so, I'm clueless what to do next.  I

do know that c ^ - 4 = 1/c^4 but don't know if this helps at all here.


Any advice would be much appreciated, Thank you, Shaynelle


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