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 Post subject: find the 20th term
PostPosted: Thu, 12 Jan 2012 22:20:57 UTC 
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what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it


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 Post subject: Re: find the 20th term
PostPosted: Thu, 12 Jan 2012 22:22:35 UTC 
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Akarion wrote:
what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it


Are you given any other information? From what you have given us the next term could literally be ANYTHING. Do you know if the sequence is supposed to be arithmetic, for instance?

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 Post subject: Re: find the 20th term
PostPosted: Thu, 12 Jan 2012 22:24:48 UTC 
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the answers to choose from are 32,44,46 and yes arithmetic sequence


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 Post subject: Re: find the 20th term
PostPosted: Fri, 13 Jan 2012 02:17:31 UTC 
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Are you too busy to do some work on this?
You could use google; you'd get sites like:
http://www.mathguide.com/lessons/Sequen ... metic.html

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 Post subject: Re: find the 20th term
PostPosted: Fri, 13 Jan 2012 05:50:53 UTC 
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Shadow wrote:
Akarion wrote:
what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it


Are you given any other information? From what you have given us the next term could literally be ANYTHING. Do you know if the sequence is supposed to be arithmetic, for instance?


It's just sequential - should be 32.

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 Post subject: Re: find the 20th term
PostPosted: Fri, 13 Jan 2012 06:11:27 UTC 
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muckman wrote:
Shadow wrote:
Akarion wrote:
what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it


Are you given any other information? From what you have given us the next term could literally be ANYTHING. Do you know if the sequence is supposed to be arithmetic, for instance?


It's just sequential - should be 32.


Wrong, a sequence is not always arithmetic. And in support of my claim, I refer you to the Lagrange interpolation theroem.

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 Post subject: Re: find the 20th term
PostPosted: Fri, 13 Jan 2012 07:12:05 UTC 
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the nth term formula is ---> (2n-8) where n is the term.

substitute 20 in the formula and you get 32.


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 Post subject: Re: find the 20th term
PostPosted: Fri, 13 Jan 2012 07:42:00 UTC 
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simonsmith wrote:
the nth term formula is ---> (2n-8) where n is the term.

Why are you calling that a "formula"?

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 Post subject: Re: find the 20th term
PostPosted: Fri, 13 Jan 2012 07:45:40 UTC 
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Denis wrote:
simonsmith wrote:
the nth term formula is ---> (2n-8) where n is the term.

Why are you calling that a "formula"?


It is, of course, one of many possible formulas for that sequence, and if the op starts his sequences with n=1, and if the poster adds "a_n=" and means to say that with the knowledge that it is supposed to be arithmetic.

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 Post subject: Re: find the 20th term
PostPosted: Fri, 13 Jan 2012 16:55:26 UTC 
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Akarion wrote:
what is the 20th term of the following sequence;
-6,-4,-2,0

please show the equation for it


Hello,Akarion.

According to: $a_n=a_1+(n-1)d

if a_1=-6\;\;\;\;,a_2=-4\;\;\;\;,a_3=-2\;\;\;\;\text{and}\;\;\;\;\;a_4=0

\text{we have:}

$a_3=a_1+(3-1)d

$-2=-6+(3-1)d

$-2=-6+2d

$-2+6=2d

$4=2d

$d=\frac{4}{2}\;\;=>\;\;d=2

So the difference is 2.

According to: $a_n=a_1+(n-1)d

\text{We have:}

$a_{20}=-6+(20-1)2

$a_{20}=-6+19*2

$a_{20}=-6+38

$a_{20}=32

like Shadow said:

Shadow wrote:
It is, of course, one of many possible formulas for that sequence, and if the op starts his sequences with n=1, and if the poster adds "a_n=" and means to say that with the knowledge that it is supposed to be arithmetic.


If it is arithmetic and if $a_1=-6 this is it. If is not ar. or anything else. Good Luck!


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 Post subject: Re: find the 20th term
PostPosted: Fri, 13 Jan 2012 18:42:39 UTC 
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Well, Ma and Pa Kettle style, you're starting with -6, and by time you get to 20th,
you'll add 19*2 = 38; 38 - 6 = 32

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 Post subject: Re: find the 20th term
PostPosted: Fri, 13 Jan 2012 20:46:05 UTC 
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Denis wrote:
Well, Ma and Pa Kettle style, you're starting with -6, and by time you get to 20th,
you'll add 19*2 = 38; 38 - 6 = 32


Let's leave Ma and Pa out of this, if I recall they think that 25/5=14.

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