# L'Hospital for this?

• Nov 12th 2008, 11:12 PM
tabularasa
L'Hospital for this?
Very basic question. Van I user L-Hosptial rule there:
(sorry about lack of latex here)

when lim x->0 the f(x) 5x^2 / 3x reaches to?
• Nov 12th 2008, 11:13 PM
Moo
Quote:

Originally Posted by tabularasa
Very basic question. Van I user L-Hosptial rule there:
(sorry about lack of latex here)

when lim x->0 the f(x) 5x^2 / 3x reaches to?

Hmmm just simplify :
$\displaystyle x^2=x*x$

$\displaystyle \implies \frac{5x^2}{3x}=\frac{5 x*x}{3x}=\frac{5x}{3}$

I'm sorry to say, but you'll have to drop this habit of always relying on l'Hospital's rule (Surprised)
• Nov 12th 2008, 11:14 PM
11rdc11
Quote:

Originally Posted by tabularasa
Very basic question. Van I user L-Hosptial rule there:
(sorry about lack of latex here)

when lim x->0 the f(x) 5x^2 / 3x reaches to?

Yes
• Nov 12th 2008, 11:15 PM
tabularasa
Could you give me example for this equation since I try to use L'Hospital I just get:

using L'H:
f'(x) / g'(x) = 10x/3

and L'H again I get:
10/?
• Nov 12th 2008, 11:16 PM
11rdc11
Quote:

Originally Posted by tabularasa
Sorry about typo. So I want to use L'Hospital rule in equation above. Is L'Hospital eligible here?

Yes
• Nov 12th 2008, 11:20 PM
tabularasa
Quote:

Originally Posted by Moo
Hmmm just simplify :
$\displaystyle x^2=x*x$

$\displaystyle \implies \frac{5x^2}{3x}=\frac{5 x*x}{3x}=\frac{5x}{3}$

I'm sorry to say, but you'll have to drop this habit of always relying on l'Hospital's rule (Surprised)

Heh, so I cant use L'Hospital here? One say Yes and you show me that no it is not usable in this?

EDIT: Ah, I see, the equation is not in a form where L'Hospital rule works with. Not in 0/0 or infinity/infinity form since 5x^2/3x = 5x/3
Thanks!
• Nov 12th 2008, 11:23 PM
Moo
Quote:

Originally Posted by tabularasa
Heh, so I cant use L'Hospital here? One say Yes and you show me that no it is not usable in this?

You can use it ! Because both numerator and denominator go to 0..

But it's not the most suitable method here. If you're not specifically asked to use l'Hospital's rule in this case, then don't. Simplify first.
Your first question "Can I use" is ambiguous ^^'
• Nov 12th 2008, 11:25 PM
11rdc11
Quote:

Originally Posted by tabularasa
Heh, so I cant use L'Hospital here? One say Yes and you show me that no it is not usable in this?

Both ways are correct, notice you get the same answer.
• Nov 12th 2008, 11:45 PM
tabularasa
Ok, could you help me on this.

After use L'H once for 5x^2/3x I will get: 10x/3
What next?
• Nov 13th 2008, 12:05 AM
mr fantastic
Quote:

Originally Posted by tabularasa
Ok, could you help me on this.

After use L'H once for 5x^2/3x I will get: 10x/3
What next?

Now take the limit x --> 0 (!)
• Nov 13th 2008, 12:29 AM
tabularasa
Aargh! It was too obvious. 0/3
Thanks you guys! (Bow)