# Homework Help: L hopital

1. Jun 24, 2007

### sacwchiri

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 im not sure if you can use it to solve this...

2. Jun 24, 2007

### ice109

you have to put expression as the ratio of two functions first

like this

$$\frac{x^3}{e^{x^2}}$$

then you can apply l'hospitale

3. Jun 24, 2007

### sacwchiri

yeah i thought about that but amm not sure how much is e^-infinite

4. Jun 24, 2007

### cepheid

Staff Emeritus
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. Jun 25, 2007

### HallsofIvy

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?

Last edited by a moderator: Jun 25, 2007