Tried using L'Hopital and I know that's what you have to use but I still get stuck here..

What am I doing wrong?

Printable View

- February 10th 2011, 09:14 PMqleeq[SOLVED]Need a method for solving this..

Tried using L'Hopital and I know that's what you have to use but I still get stuck here..

What am I doing wrong? - February 10th 2011, 09:17 PMharish21
You did not take the derivative of the denominator while using Lhopital's rule!

- February 10th 2011, 09:20 PMguildmage
Aren't you also supposed to take the derivative of the denominator?

You just replaced with - February 10th 2011, 09:24 PMqleeq
- February 10th 2011, 09:34 PMharish21
.

use Lhopitals rule to get:

use Lhopitals rule once again to get the answer. - February 10th 2011, 09:35 PMProve It
This goes to , so you can use L'Hospital's Rule again. Also note that , which will make differentiating the denominator easier...

- February 10th 2011, 10:15 PMqleeq
- February 10th 2011, 10:16 PMharish21
- February 10th 2011, 10:33 PMqleeq
Must have accidentally removed them while I was editing.. Anyway, thanks a lot for your help. I had one last question though.

Can you explain to me how he arrived at the firstequation from ?

I understand the second part, but the first part has me confused.

How did he get from ?

I understand the sin(2x) = 2sin(x)cos(x) part. - February 10th 2011, 10:41 PMharish21

- February 10th 2011, 10:42 PMqleeq
- February 10th 2011, 11:27 PMProve It
Actually, in this case it's easier to use L'Hospital's Rule the second time BEFORE doing any algebraic manipulation...

by L'Hospital's Rule.

The limit is now evaluated through direct substitution.