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PostPosted: Thu Nov 08, 2012 6:31 pm 
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For this sequence work out the next term, the rule, the nth term and then work out the 50th term:

15, 11, 7, 3

next term:..........

rule:....................

nth term:............

50th term:.........


Many thanks. Could you explain to me what the nth term means?


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PostPosted: Thu Nov 08, 2012 8:06 pm 
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explanation deleted, :oops: :oops: realised I was talking rubbish!


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PostPosted: Thu Nov 08, 2012 8:39 pm 
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What does nth term mean?


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PostPosted: Thu Nov 08, 2012 8:42 pm 
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use this link, my answer was wrong, apologies

http://mathcentral.uregina.ca/QQ/databa ... alex1.html


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PostPosted: Thu Nov 08, 2012 8:56 pm 
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Can I respectfully disagree? If you say the rule for the nth term is n-4 then the 50th term would be 50-4 = 46.


I agree that you take away 4 to get to the next number in the sequence, so would say that the rule is take away 4 to get to the next term.

But to get the nth term don't you need to work out a formula for the nth term? - and for that you need to show that the first number in the sequence is 15.

I would say that the formula for the nth term is: 19 - 4n

Term 1: 19 - 4(1)
=19 - 4
= 15

Term 2: 19 - 4(2)
= 19 - 8
= 11

Term 3: 19 - 4(3)
= 19 -12
= 7

So, for the 50th term: 19 - 4(50)
= 19 - 200
= -181

Unfortunately I'm not a teacher so I don't know how to show you to get to the formula in the first place. I think Ds would try it as 15-4n or something, realise that didn't work and then get to 19-4n. That's not a great way to teach to apply on other questions though, sorry.

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PostPosted: Thu Nov 08, 2012 9:16 pm 
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by all means disagree!


must admit it was a quick answer..!


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PostPosted: Thu Nov 08, 2012 10:04 pm 
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yoyo123 wrote:


The link you quote is correct. Your summary of it isn't.


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PostPosted: Thu Nov 08, 2012 10:10 pm 
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Pumpkin Pie wrote:
What does nth term mean?


n=1 for the first term, 2 for the second term, etc. Hence, as JRM says, the rule is 19-4n (if you were writing it formally, it would be something like x subscript n = 19 - 4n).

An arithmetic sequence (those where the difference between successive terms is constant) will be of the form x sub n = a + bn. You can get b simply by looking at the difference between terms, and is here -4. Then you solve for a: you've got 15 = b - 4x1, so b is 19.


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PostPosted: Thu Nov 08, 2012 10:41 pm 
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May I ask, what year homework is this? Year 5? Or 6?

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PostPosted: Thu Nov 08, 2012 10:45 pm 
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The common difference between terms in -4 so the rule must be based on the -4 times table ie one part must be -4xn

We then need to make the rule fit starting at 15 ... so the nth term is 19-4n

OK?


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