Derivatives Of Log. Functions... HELP!!! Calculus II is a Bitch! - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Insert BS here A place to discuss anything you want

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 11-02-2007, 08:08 PM   #1
Elite Member
Thread Starter
iTrader: (15)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,797
Total Cats: 248
Default Derivatives Of Log. Functions... HELP!!! Calculus II is a Bitch!

I cant figure out derivatives of Logarithmic functions. Here's an example from my notes.


Problem: Y=ln(x^4(sin^2(x))) Find first derivative.

Y= ln(x^4) + ln(sin^2(x)) dx

Y= ln(x^4) + ln(sin(x))^2 dx

Y=4ln(x) + 2ln(sinx) dx

I get here, then I get stuck.

Y'= ???

My notes show Y'= (4/x) + (2cos(x))/(sin(x) But I don't see how they got that.

I'm pretty sure you have to use chain rule to get this answer, but I don't know I'm just not getting it.

I've even tried some of the online calculus calculators and they come up with different answers then the one from my notes.

Thanks for any help.
patsmx5 is offline   Reply With Quote
Old 11-02-2007, 08:52 PM   #2
Senior Member
 
Join Date: Mar 2006
Posts: 1,379
Total Cats: 1
Default

My personal opinion. Become a psychologist... the math is easier!

Mark
Markp is offline   Reply With Quote
Old 11-02-2007, 09:24 PM   #3
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

I'm with Mark, i stopped at Calc 1 for a reason.
cjernigan is offline   Reply With Quote
Old 11-02-2007, 09:25 PM   #4
Senior Member
iTrader: (2)
 
SamS's Avatar
 
Join Date: Jun 2006
Location: Wisconsin
Posts: 1,254
Total Cats: 7
Default

:gay: I made a thread here about hating Calc II last semester. I'll be taking it again next semester.

Edit: and I don't remember how to derive log functions either
SamS is offline   Reply With Quote
Old 11-02-2007, 09:30 PM   #5
Elite Member
iTrader: (6)
 
Loki047's Avatar
 
Join Date: Sep 2005
Location: Chicago
Posts: 4,145
Total Cats: 0
Default

'(ln(x))=1/x

Which gives you 2(sin(x)/x)
now go to your law of cos and sin
Loki047 is offline   Reply With Quote
Old 11-02-2007, 09:32 PM   #6
Elite Member
iTrader: (3)
 
Mach929's Avatar
 
Join Date: Oct 2004
Location: lansdale PA
Posts: 2,500
Total Cats: 0
Default

lol well once upon a time i could help you but well i don't remember anymore, sorry, what is your major?
Mach929 is offline   Reply With Quote
Old 11-02-2007, 09:49 PM   #7
Elite Member
iTrader: (3)
 
Join Date: May 2006
Location: Houston, TX
Posts: 2,900
Total Cats: 0
Default

my text book had a log derivatives table with general rules and such... made it so easy that I couldn't possibly do it without my book.... which is at the office, so you are out of luck,
Arkmage is offline   Reply With Quote
Old 11-02-2007, 10:09 PM   #8
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

I should line you out with my roommate, he's a double major, ME and Math.
Took calc 3 and dif-e the same semster, said it was a breeze. He finally has a hard class in school, dif-e 2 is making him hate life.
cjernigan is offline   Reply With Quote
Old 11-02-2007, 10:24 PM   #9
Elite Member
Thread Starter
iTrader: (15)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,797
Total Cats: 248
Default

Quote:
Originally Posted by Arkmage View Post
my text book had a log derivatives table with general rules and such... made it so easy that I couldn't possibly do it without my book.... which is at the office, so you are out of luck,
Thank you. Turns out my text book has Rules too. I don't know why but I just didn't see them before. I've got this figured out now, I just needed the rules to follow.

I didn't know there was a diff. between x^n and a^x. Of course, there is, and there are diff. rules for each. That was the main thing I was overlooking.

My major is Mechanical Engineering. This is my second year and next semester I'll be taking Calculus III, Linear Algerbra, Physics II, and Statics. I'm not exactly looking forward to it. The physics comes easy, but this calculus gets me triped up pretty regularly.

Loki, I see that lnx dx = 1/x, but I didn't follow the rest of that. Anyway, I've a few rules to use and so far they're working.
patsmx5 is offline   Reply With Quote
Old 11-02-2007, 11:00 PM   #10
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

When i was in calc my book had all of the rules on in the back 2 pages and on the back of the rear cover.
cjernigan is offline   Reply With Quote
Old 11-02-2007, 11:12 PM   #11
Elite Member
Thread Starter
iTrader: (15)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,797
Total Cats: 248
Default

Quote:
Originally Posted by cjernigan View Post
When i was in calc my book had all of the rules on in the back 2 pages and on the back of the rear cover.


Damn it again. Sure enough, there's 3 pages of formulas back their I could have been using since Cal I. I guess I just never thought to look there.

Oh well, at least I've got all the people on this forum to set me straight.
patsmx5 is offline   Reply With Quote
Old 11-02-2007, 11:14 PM   #12
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

Seriously, without those 3 pages i would have failed. Xerox those pages and put them in your notebook, on your wall, your g/fs wall. Just so you know as many of them as possible.
cjernigan is offline   Reply With Quote
Old 11-02-2007, 11:21 PM   #13
Elite Member
Thread Starter
iTrader: (15)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,797
Total Cats: 248
Default

Quote:
Originally Posted by cjernigan View Post
Seriously, without those 3 pages i would have failed. Xerox those pages and put them in your notebook, on your wall, your g/fs wall. Just so you know as many of them as possible.
Yeap. I have a copy in my notebook now. That should definately help.
patsmx5 is offline   Reply With Quote
Old 11-02-2007, 11:22 PM   #14
Ben
Supporting Vendor
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

Loki, how do you remember how to do that?
Ben is offline   Reply With Quote
Old 11-02-2007, 11:56 PM   #15
Elite Member
iTrader: (2)
 
Join Date: Jan 2007
Location: Lexington, SC
Posts: 2,084
Total Cats: 0
Default

i hate that ****, I'm doin absolute maxima and minima in calc. I now, dy/dx and limits ftl
mazda/nissan is offline   Reply With Quote
Old 11-03-2007, 12:00 AM   #16
Ben
Supporting Vendor
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

Quote:
Originally Posted by mazda/nissan View Post
i hate that ****, I'm doin absolute maxima and minima in calc. I now, dy/dx and limits ftl
I though it was hard at the time too, but actually it's just the foundation for the hard stuff that comes later. You'll get really good and really fast at it.
Wait until when (if) you get to the multivariate stuff. Ugh.
Ben is offline   Reply With Quote
Old 11-03-2007, 12:04 AM   #17
Elite Member
iTrader: (2)
 
Join Date: Jan 2007
Location: Lexington, SC
Posts: 2,084
Total Cats: 0
Default

Quote:
Originally Posted by Ben View Post
multivariate stuff
i just can't wait
I've also got a lab that uses Maple 11 software with my TA Arnab, but i see it as miataturbo.net time
mazda/nissan is offline   Reply With Quote
Old 11-03-2007, 12:12 AM   #18
y8s
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
 
y8s's Avatar
 
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,038
Total Cats: 407
Default

you'll need to know that calc when you start taking the heat transfer and control system stuff. it's pretty useful.
y8s is offline   Reply With Quote
Old 11-03-2007, 12:50 AM   #19
Elite Member
iTrader: (12)
 
Join Date: Jan 2007
Location: Hermosa Beach, CA
Posts: 2,575
Total Cats: 11
Default

oh goodie, this is what I have to look foward too next year when im a mechanical enginneer in college! woo hoo..
cardriverx is offline   Reply With Quote
Old 11-03-2007, 03:28 AM   #20
Senior Member
 
Join Date: Jun 2005
Location: WA
Posts: 500
Total Cats: 0
Default

Stop posting this, it makes not want to go to school
RusMan is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Missing/knock at idle, can someone point me in the right direction? Mikel MEGAsquirt 4 09-28-2015 05:46 PM
Air Coolant Correction 86-145 iparnell MEGAsquirt 2 09-13-2015 08:04 PM
It runs! But not well.. Input appreciated. viriiguy MEGAsquirt 10 09-04-2015 07:28 PM
$94K nissan? TonyC Insert BS here 46 09-28-2007 06:47 AM
Does anyone actually use calculus? SamS Insert BS here 52 03-31-2007 09:39 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 06:19 AM.