- #1
Easy_as_Pi
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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[itex]\in[/itex] natural numbers, a[itex]_{n+1}[/itex] [itex]\geq[/itex]a[itex]_{n}[/itex] 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[itex]_{n+1}[/itex] - a[itex]_{n}[/itex] is decreasing or eventually decreasing for all n.
So, ideally, I'd end up with something like -x[itex]^{2}[/itex] after a[itex]_{n+1}[/itex] - a[itex]_{n}[/itex]. 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!