Sequence and Series question (maybe)?

In summary, the conversation discusses how to find all positive integers n that satisfy the condition that both n+2008 and n+2009 divide n^2+2008 and n^2+2009, respectively. The conversation explores different attempts at solving the problem, eventually reaching the conclusion that there are no such integers that satisfy the condition.
  • #1
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Homework Statement



Find all positive integers n such that both n + 2008 divides n^2 + 2008 and n + 2009 divides n^2 + 2009

Homework Equations



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The Attempt at a Solution



I have no idea where to start... I'm not even sure it's a sequence and series question. If it is then I have no idea what to do.
I've played around with it by saying (n^2+2008)/(n+2008)=a and (n^2+2009)/(n+2009)=b, rearranging them into quadratics and equating them, then rearranging again in terms of n. Doing this I got n=(-2008a+2009b-1)/(a-b) and couldn't see anything to do from this. I did a similar thing using partial fractions but ended up with pretty much the same equation (though not exactly the same so I could well have done something wrong but I don't think that was the right way to go about it anyway).
Any light that anyone can shed on this would be much appreciated :)
 
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  • #2
One way that n+2008 could divide n^2+2008 is that n+2008=n^2+2008. But then n=0 or n=1.

Assume that n+2008 divides n^2+2008. Then n+2008 also divides (n^2+2008)-(n+2008). Thus n+2008 divides n^2-n.
Now do thesame for n+2009, what do you get?
 
  • #3
I get n+2009 divides n^2-n.
I see that they have the same numerator... Though dividing n+2008 and n+2009 to get rid of n^2 - n won't necessarily give another integer so I'm guessing that's not the next step. I had a play around after doing this and got n^2 - n = n^2 - n which also isn't much help...!
This is a little embarrassing :blushing:
 
  • #4
Yes, and since gcd(n+2008,n+2009)=1. We must have that (n+2008)(n+2009) divides n^2-n. This is a contradiction.
 
  • #5
Yes I see it now, thanks for the help :)
 

1. What is a sequence and series?

A sequence is a list of numbers that follow a certain pattern or rule. A series is the sum of the terms in a sequence.

2. How do you determine the next term in a sequence?

To determine the next term in a sequence, you need to identify the pattern or rule that the sequence follows. This can involve finding the difference between consecutive terms, or using a formula to generate the terms.

3. What is the difference between an arithmetic and geometric sequence?

An arithmetic sequence has a constant difference between consecutive terms, while a geometric sequence has a constant ratio between consecutive terms. In other words, in an arithmetic sequence, you add the same value to each term to get the next term, while in a geometric sequence, you multiply each term by the same value to get the next term.

4. How do you find the sum of a finite arithmetic or geometric series?

The sum of a finite arithmetic series can be found using the formula Sn = n/2(a₁ + an), where n is the number of terms, a₁ is the first term, and an is the last term. The sum of a finite geometric series can be found using the formula Sn = a₁(1-rⁿ)/(1-r), where a₁ is the first term, r is the common ratio, and n is the number of terms.

5. How are sequences and series used in real life?

Sequences and series are used in various fields such as mathematics, physics, engineering, and economics to model and analyze real-life situations. For example, arithmetic sequences can be used to model the growth of a population, while geometric series can be used to calculate compound interest. They are also used in computer algorithms and data compression techniques.

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