WHY lim{x-> infinity} f(x)/x = infinity => lim{x-> infinity} f(x) = infinity ?

  • Thread starter gymko
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In summary, the first limit being infinity indicates that f(x) is growing at a faster rate than x is. This is evidence for the fact that lim f(x) must be infinity as well. To prove this, further analysis and evidence would be needed.
  • #1
gymko
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Homework Statement



Why is it?
lim{x-> infinity} f(x)/x = infinity => lim{x-> infinity} f(x) = infinity

What is evidence?

Thank you very much.
 
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  • #2
The reason this is so is that the first limit being infinity implies that f(x) is growing at a faster rate than x is.

As for evidence, if you assume that lim f(x) is finite or doesn't exist, then lim [f(x)/x] is 0 or doesn't exist as x gets large, which is a contradiction. If you were going to prove this, you would have to be a little more careful, but maybe you get the idea I'm trying to convey.
 

1. Why does the limit of f(x)/x as x approaches infinity equal infinity?

The limit of f(x)/x as x approaches infinity equals infinity because as x gets larger and larger, the value of f(x) also gets larger. Since the denominator is approaching infinity, the quotient will also approach infinity.

2. How does the limit of f(x) as x approaches infinity relate to the limit of f(x)/x as x approaches infinity?

The limit of f(x) as x approaches infinity is directly related to the limit of f(x)/x as x approaches infinity. In fact, the limit of f(x)/x can be found by dividing the limit of f(x) by the limit of x. This is because as x gets larger, the value of x becomes insignificant compared to the value of f(x).

3. Can the limit of f(x) as x approaches infinity be equal to infinity if the limit of f(x)/x as x approaches infinity does not exist?

No, the limit of f(x) as x approaches infinity cannot be equal to infinity if the limit of f(x)/x as x approaches infinity does not exist. This is because if the limit of f(x)/x does not exist, it means that the quotient does not approach a specific value as x gets larger. Therefore, the limit of f(x) cannot approach a specific value, and thus cannot equal infinity.

4. Are there any cases where the limit of f(x) as x approaches infinity can be equal to infinity even if the limit of f(x)/x as x approaches infinity is not infinity?

Yes, there are cases where the limit of f(x) as x approaches infinity can equal infinity even if the limit of f(x)/x as x approaches infinity is not infinity. This can happen if the limit of f(x)/x approaches infinity from one side and negative infinity from the other side. In this case, the limit of f(x) would still be equal to infinity as x approaches infinity, even though the limit of f(x)/x does not exist.

5. Is it possible for the limit of f(x) as x approaches infinity to equal a value other than infinity?

Yes, it is possible for the limit of f(x) as x approaches infinity to equal a value other than infinity. This can happen if the limit of f(x)/x approaches a finite value or if the limit of f(x)/x approaches zero. In these cases, the limit of f(x) would be equal to the same value as the limit of f(x)/x multiplied by infinity or zero, respectively.

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