Product of 2 Increasing Sequences Not Necessarily Increasing

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SUMMARY

The discussion centers on demonstrating that the product of two eventually increasing sequences is not necessarily eventually increasing. A counterexample is provided using the sequence -1/n, which is eventually increasing despite its negative values. The key takeaway is that one must consider sequences that include negative values to illustrate this concept effectively. The participants emphasize the importance of understanding the definition of eventually increasing sequences and how to construct counterexamples.

PREREQUISITES
  • Understanding of sequences and series in mathematics
  • Familiarity with the concept of eventually increasing sequences
  • Knowledge of proof techniques, particularly proof by counterexample
  • Basic algebraic manipulation and function behavior analysis
NEXT STEPS
  • Explore the properties of eventually increasing sequences in detail
  • Learn about counterexamples in mathematical proofs
  • Study the behavior of negative sequences and their implications
  • Investigate the relationship between sequence convergence and divergence
USEFUL FOR

Students in advanced mathematics courses, particularly those studying sequences and series, as well as educators seeking to illustrate the nuances of sequence behavior in mathematical proofs.

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Homework Statement


Give an example to show that it is not necessarily true that the product of two eventually increasing sequences is eventually increasing.


Homework Equations


a sequence is eventually increasing if for N\in natural numbers, a_{n+1} \geqa_{n} for all n>N.


The Attempt at a Solution


So, I know this is merely proof by counterexample. I find one example to show that the product of two eventually increasing sequences is not necessarily eventually increasing. The only catch is that I have no idea where to start. There are infinitely many eventually increasing sequences I could multiply together. I know the end goal is to show that a_{n+1} - a_{n} is decreasing or eventually decreasing for all n.
So, ideally, I'd end up with something like -x^{2} after a_{n+1} - a_{n}. I don't want a specific example which will solve this problem. Some guidance as to where to begin would be greatly appreciated, though!
Thanks!
 
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Try picking an eventually increasing sequence whose values are negative.
 
Sorry that I took an eternity to reply. I was at a study session for linear algebra. Thanks so much, Dick. I think you've helped on every question I've posted here. I really appreciate it. I tripped myself up by only thinking about positive sequences. I took increasing and mistakenly correlated it with positive, too. Immediately after your hint, I thought about -1/n, and then found my solution. This series and sequences course has managed to confuse me more than any previous math class.
 

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