Derivative help

k_rock923 · 8th June 2004, 01:31

I know that the derivative os cos(4x) is -4sin(4x). . .so does that mean that you just take the four out and put it in front of the derivative of cos?

And i can't figure out for anything how to do 3xsin(3x)

cyu · 8th June 2004, 01:43

(3x)(derivative of sin(3x))+(sin3x)(3)

I took calc last year.

k_rock923 · 8th June 2004, 01:44

that doesn't help because i get stuck on derivative of sin(3x)

edit/ is 3sin(3x) + 9xcos(3x) the final answer?

cyu · 8th June 2004, 01:58

Yep. looks right.

griffinn · 8th June 2004, 02:01

code:
  d (3x sin 3x) / dx

= [d(3x) / dx] * [d (3x sin 3x) / d(3x)]

= 3 * { 3x [d(sin 3x)]/d(3x) + sin 3x * [3x/d(3x)] }

= 3 * ( 3x cos 3x + sin 3x )

= 9x cos 3x + 3 sin 3x

So yeah, it's correct.

ElChevelle · 8th June 2004, 02:10

I concur.

k_rock923 · 8th June 2004, 02:17

something like x(2sinxcosx) becomes 2xsinxcosx right? why is only the 2 multiplied by the x?

griffinn · 8th June 2004, 02:19

That's the associative property of multiplication. Basic algebra.

deeder7001 · 8th June 2004, 02:22

i don't remember how to do advanced math anymore. it's been about a year since i've been in a math class.

k_rock923 · 8th June 2004, 02:23

thanks guys. once again, basic algebra ruins an otherwise correct problem

cyu · 8th June 2004, 02:25

Quote:

Originally posted by k_rock923
something like x(2sinxcosx) becomes 2xsinxcosx right? why is only the 2 multiplied by the x?

are you talking about the derivative of that?

k_rock923 · 8th June 2004, 02:30

no. that was part of the answer to xsinsquaredx
so it was x(2sinxcosx)+(sin squared x)1
and that turned into 2xsinxcosx + sin^2 x

if that's wrong, please tell me.

ryan · 8th June 2004, 02:56

Ask in the AVS forums, they could most likely help.

griffinn · 8th June 2004, 02:59

Sssshhhh... he's got it right, but we're not supposed to tell him!

/me hides

Hollow · 8th June 2004, 03:59

k_rock, look up the chain rule in your book. If you don't get it from the book, find someone to show you how it works until you get it. Have random people tell you if you got one question right without understanding the mechanism is wasting your time and ours.

k_rock923 · 8th June 2004, 19:51

hollow, thats how i solved it. i'm just making sure that i did it right. thanks though.

8th June 2004, 01:31	#1
k_rock923 \m/ (Forum King) Join Date: Jul 2003 Location: /bin/bash Posts: 7,786	Derivative help I know that the derivative os cos(4x) is -4sin(4x). . .so does that mean that you just take the four out and put it in front of the derivative of cos? And i can't figure out for anything how to do 3xsin(3x) Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.

8th June 2004, 01:44	#3
k_rock923 \m/ (Forum King) Join Date: Jul 2003 Location: /bin/bash Posts: 7,786	that doesn't help because i get stuck on derivative of sin(3x) edit/ is 3sin(3x) + 9xcos(3x) the final answer? Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.

8th June 2004, 02:01	#5
griffinn Court Jester (Forum King) Join Date: May 2000 Location: Your local toystore Posts: 3,502	code: d (3x sin 3x) / dx = [d(3x) / dx] * [d (3x sin 3x) / d(3x)] = 3 * { 3x [d(sin 3x)]/d(3x) + sin 3x * [3x/d(3x)] } = 3 * ( 3x cos 3x + sin 3x ) = 9x cos 3x + 3 sin 3x So yeah, it's correct. The smiley slot machine! \| Quotable Blog

8th June 2004, 02:17	#7
k_rock923 \m/ (Forum King) Join Date: Jul 2003 Location: /bin/bash Posts: 7,786	something like x(2sinxcosx) becomes 2xsinxcosx right? why is only the 2 multiplied by the x? Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.

8th June 2004, 02:19	#8
griffinn Court Jester (Forum King) Join Date: May 2000 Location: Your local toystore Posts: 3,502	That's the associative property of multiplication. Basic algebra. The smiley slot machine! \| Quotable Blog

8th June 2004, 01:43	#2
cyu Major Dude Join Date: Apr 2002 Location: in front of my pc Posts: 1,617	(3x)(derivative of sin(3x))+(sin3x)(3) I took calc last year.

8th June 2004, 01:58	#4
cyu Major Dude Join Date: Apr 2002 Location: in front of my pc Posts: 1,617	Yep. looks right.

8th June 2004, 02:10	#6
ElChevelle Moderator Alumni Join Date: Jun 2000 Location: the MANCANNON! Posts: 22,431	I concur.

8th June 2004, 02:22	#9
deeder7001 Jesus Freak (Forum King) Join Date: Aug 2002 Location: Austin, TX Posts: 5,455	i don't remember how to do advanced math anymore. it's been about a year since i've been in a math class. There is no sig.

8th June 2004, 02:23	#10
k_rock923 \m/ (Forum King) Join Date: Jul 2003 Location: /bin/bash Posts: 7,786	thanks guys. once again, basic algebra ruins an otherwise correct problem Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.

8th June 2004, 02:30	#12
k_rock923 \m/ (Forum King) Join Date: Jul 2003 Location: /bin/bash Posts: 7,786	no. that was part of the answer to xsinsquaredx so it was x(2sinxcosx)+(sin squared x)1 and that turned into 2xsinxcosx + sin^2 x if that's wrong, please tell me. Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.

8th June 2004, 02:56	#13
ryan not fucked, not quite. (Forum King) Join Date: Feb 2002 Location: Tn Posts: 8,755	Ask in the AVS forums, they could most likely help.

8th June 2004, 02:59	#14
griffinn Court Jester (Forum King) Join Date: May 2000 Location: Your local toystore Posts: 3,502	Sssshhhh... he's got it right, but we're not supposed to tell him! /me hides The smiley slot machine! \| Quotable Blog

8th June 2004, 03:59	#15
Hollow Major Dude Join Date: Oct 2001 Location: Baker Lab, Ithaca NY Posts: 1,128	k_rock, look up the chain rule in your book. If you don't get it from the book, find someone to show you how it works until you get it. Have random people tell you if you got one question right without understanding the mechanism is wasting your time and ours. The moon is made of cheese. Oh for some tasty moon cheese. www.redtetrahedron.org

8th June 2004, 19:51	#16
k_rock923 \m/ (Forum King) Join Date: Jul 2003 Location: /bin/bash Posts: 7,786	hollow, thats how i solved it. i'm just making sure that i did it right. thanks though. Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.

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