Solving an Infinite Limit with L'Hôpital's Rule

In summary, the conversation discusses using L'Hopital's rule to solve the problem of finding the limit of x^3 * e^(-x^2) as x approaches infinity. It is suggested to rewrite the expression as a ratio of two functions and then apply the rule. There is also a clarification about the behavior of e^x as x approaches infinity.
  • #1
sacwchiri
7
0
Im trying to solve this problem using l'hopital but amm not sure how to do it

lim
X->infinite x^3 * e^(-x^2)

soo this infinite * e^-infinite... but from there I am not sure if you can use it to solve this...
 
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  • #2
sacwchiri said:
Im trying to solve this problem using l'hopital but amm not sure how to do it

lim
X->infinite x^3 * e^(-x^2)

soo this infinite * e^-infinite... but from there I am not sure if you can use it to solve this...
you have to put expression as the ratio of two functions first

like this

[tex] \frac{x^3}{e^{x^2}}[/tex]

then you can apply l'hospitale
 
  • #3
yeah i thought about that but amm not sure how much is e^-infinite
 
  • #4
sacwchiri said:
yeah i thought about that but amm not sure how much is e^-infinite

This question makes no sense.

As ice109 said, apply L'Hospital's rule. Do you know what L'Hospital's rule is? If so, apply it to this question.
 
  • #5
sacwchiri said:
yeah i thought about that but amm not sure how much is e^-infinite
That sounds like you are saying "how infinite is it"! What you mean is "what number is e^-infinite". (Strictly speaking that is also meaningless- you cannot evaluate a function of real numbers "at infinity", you can only take limits at infinity.) You know, I hope, that e^x increases without bound (i.e. "goes to infinity") as x goes to infinity. You should also know that "e^(-x2) MEANS 1/e^(x2). If A goes to infinity, what does 1/A go to?
 
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What is L'Hôpital's Rule?

L'Hôpital's Rule is a mathematical theorem used to solve indeterminate forms in calculus, particularly in finding limits of functions. It states that for certain types of limits, the limit of the ratio of two functions is equal to the limit of their derivatives.

When should L'Hôpital's Rule be used?

L'Hôpital's Rule is used when evaluating limits that result in indeterminate forms such as 0/0 or ∞/∞. It can also be used when evaluating limits of the form 0 x ∞.

What are the steps to solve an infinite limit using L'Hôpital's Rule?

The steps for using L'Hôpital's Rule to solve an infinite limit are as follows:

  1. Identify the indeterminate form of the limit.
  2. Take the derivative of the numerator and denominator separately.
  3. Evaluate the limit of the ratio of the derivatives.
  4. If the limit still results in an indeterminate form, repeat the process until a definitive answer is obtained.

Can L'Hôpital's Rule be used for all infinite limits?

No, L'Hôpital's Rule can only be applied to certain types of infinite limits, specifically those that result in indeterminate forms such as 0/0 or ∞/∞. It cannot be used for limits that do not result in these forms.

Are there any limitations to using L'Hôpital's Rule?

Yes, L'Hôpital's Rule can only be used for functions that are differentiable in the given interval. Additionally, it can only be used for limits that result in indeterminate forms and may not always provide a definitive answer.

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