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#1 2013-06-13 12:54:18

Nikster
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Arithmetic Series - Finding Terms when given two sums

Find the first five terms of an arithmetic series with S10 = 210 and S20 = 820
S= Sum

Last edited by Nikster (2013-06-13 12:54:47)

#2 2013-06-13 13:12:04

bobbym
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Re: Arithmetic Series - Finding Terms when given two sums

Hi;

I am getting:

3, 7, 11, 15, 19, ...


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

#3 2013-06-13 13:43:38

Nikster
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Re: Arithmetic Series - Finding Terms when given two sums

I missed this class on how you do this. What process did you go through to get these numbers?

#4 2013-06-13 13:51:07

bobbym
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Re: Arithmetic Series - Finding Terms when given two sums

I solved 2 equations simultaneously: This is the formula for an artihmetic sum.



we have





this means we have 2 n's for equation1. With 2 n's we can get a1 ( the first term ) and d ( the distance between each term ). We have the 2 n's they are n =10 and n = 20.

Substituting into 1:






Clean em up:





Solving:

a1 = 3
d = 4

Can you finish up now?


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

#5 2013-06-13 14:07:44

Nikster
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Re: Arithmetic Series - Finding Terms when given two sums

I understand! Thank you so much!

#6 2013-06-13 14:11:20

bobbym
Administrator

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Re: Arithmetic Series - Finding Terms when given two sums

Hi Nikster;

Your welcome and welcome to the forum!


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.
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