Hello,

Looking at which frequency l'Hôpital's rule is used, i'd like to know what is its real utility... D'you have examples where we HAVE to use it ? And can't use anything else ?

As a memento :

If , then :

Printable View

- Apr 12th 2008, 07:56 AMMooAbout the real utility of l'Hôpital's rule
Hello,

Looking at which frequency l'Hôpital's rule is used, i'd like to know what is its real utility... D'you have examples where we HAVE to use it ? And can't use anything else ?

As a memento :

If , then :

- Apr 12th 2008, 08:00 AMangel.white
- Apr 12th 2008, 08:37 AMMoo
- Apr 12th 2008, 08:43 AMMathstud28Ok
the best example would be something like ...and knowing your style you will protest and say you need to just know its 1...but what if you didnt know that? you could do a rate of decreasing...but it is just much more in my opinion beautiful to say ...there your blatantly sardonic question is answered.

- Apr 12th 2008, 08:49 AMMathstud28Oh yeah
- Apr 12th 2008, 08:49 AMMoo
Do you know why it is 1 ?

as cos is the derivative for sin.

What do you prefer ? Showing that you can learn by heart a rule ? Or showing that you are able to use the definition of the derivative number ? - Apr 12th 2008, 08:51 AMMathstud28Ok
- Apr 12th 2008, 08:52 AMMoo
- Apr 12th 2008, 08:53 AMMoo
- Apr 12th 2008, 08:56 AMMathstud28
- Apr 12th 2008, 08:58 AMMathstud28Ok
- Apr 12th 2008, 09:01 AMMoo
I'm French, so i have the circumflex on my keyboard ;)

Quote:

Unless I looked at it wrong (which you know I do all the time ) you just differntiated and go the same result...

- Apr 12th 2008, 09:07 AMMathstud28Ok
The only problem I see with that is you would have to say what you said over 1...because you applied l'hopitals rule except instead of doing f'(x) then evaluating at 0 you jsut went straight to ...but what if you were unsure if applying that method didnt yield another indeterminate form? and about the circumflex...

- Apr 12th 2008, 09:09 AMangel.white
On the sin x / x , you can also use the squeeze theorem.

- Apr 12th 2008, 09:11 AMMooQuote:

but what if you were unsure if applying that method didnt yield another indeterminate form?

Quote:

because you applied l'hopitals rule except instead of doing f'(x) then evaluating at 0 you jsut went straight