Understanding Infinite Limits: A Formal Definition and Explanation

In summary, the limit of Xn as n->infinity being equal to infinity means that as n increases, the value of Xn also increases without bound. This can be thought of as the opposite of being bounded and can be represented using the epsilon definition in reverse or by using "x> N" for some number N.
  • #1
tony979
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Homework Statement



Give a definition to explain what it means if the limit of Xn as n->infinity is itself equal to infinity.

Homework Equations





The Attempt at a Solution



It seems the typical use of epsilon to show limits (that we approach arbitrary closeness) doesn't work here, so I had thought I could say it is the opposite of being bounded, but I'm not sure about how to say this more formally...

Thanks for any ideas you may be able to offer
 
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  • #2
tony979 said:

It seems the typical use of epsilon to show limits (that we approach arbitrary closeness) doesn't work here, so I had thought I could say it is the opposite of being bounded, but I'm not sure about how to say this more formally...


Well you mention the idea of "arbitrary closeness" using the epsilon definition. Why not think about it in terms of the arbitrary "largeness" of xn as n becomes large?
Or try to use epsilon in reverse?
 
  • #3
The "the typical use of epsilon to show limits " works fine. It is the "delta" that doesn't work! Saying that a number is "going to infinity" does mean that it is unbounded so instead of "[itex]|x- a|< \delta[/itex]" as you would with "limit as x goes to a", how about something like "x> N" for some number N.
 

1. What is the formal definition of an infinite limit?

The formal definition of an infinite limit states that the limit of a function as the input approaches a certain value is infinite if the output of the function approaches positive or negative infinity as the input gets closer and closer to that value.

2. How is an infinite limit different from a finite limit?

An infinite limit is different from a finite limit in that a finite limit has a specific value that the function approaches as the input gets closer to a certain value, whereas an infinite limit has no specific value and instead approaches positive or negative infinity.

3. What is the purpose of understanding infinite limits?

Understanding infinite limits is important in calculus and other areas of mathematics as it allows us to analyze the behavior of functions near certain points and make predictions about their behavior. It is also useful in solving various real-world problems involving rates of change and optimization.

4. How do you determine if a limit is infinite?

To determine if a limit is infinite, you must evaluate the limit as the input approaches the given value from both sides. If the output approaches positive infinity from one side and negative infinity from the other side, then the limit is infinite.

5. Can a function have more than one infinite limit?

Yes, a function can have more than one infinite limit. This occurs when the function approaches different values of positive or negative infinity as the input approaches different values. For example, the function f(x) = 1/x has infinite limits at x = 0 and x = ∞, as the output approaches positive infinity when x approaches 0 from the right and negative infinity when x approaches ∞.

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