Need help with math problem

PmbPhy · « **on:** 19/05/2018 00:37:39 »

This should be easy for me but then again that's why I'm brushing up. I.e. if you don't use it then you loose it. See attached picture. How does he do the algebra after the integration is done to get to the end? Many Thanks!!!

Image1.jpg (73.72 kB . 823x255 - viewed 2600 times)

Here's a PDF with everything.

Griffiths.pdf (449.9 kB - downloaded 233 times)

saspinski · « **Reply #1 on:** 20/05/2018 16:03:06 »

No big deal until the last simplification, when a big luck let the remaining terms, after adding and subtracting to complete (b - a)³, happen to form 3a(b - a )².

PmbPhy · « **Reply #2 on:** 20/05/2018 21:41:10 »

Quote from: saspinski on 20/05/2018 16:03:06

No big deal until the last simplification, when a big luck let the remaining terms, after adding and subtracting to complete (b - a)³, happen to form 3a(b - a )².

Thanks. But what line are you talking about? I've attached a PDF file with that part of the answer and my work.

Do you have a flatbed scanner? And can you rephrase that. Its a bit unclear to me.

jeffreyH · « **Reply #3 on:** 20/05/2018 22:30:42 »

b³-3a²b+2a³ = (b-a)²(2a+b) so that the factor of (b-a)² cancels.

PmbPhy · « **Reply #4 on:** 21/05/2018 01:28:28 »

Quote from: jeffreyH on 20/05/2018 22:30:42

b^3-3a^2b+2a^3 = (b-a)^2(2a+b) so that the factor of (b-a)^2 cancels.

That's all find and dandy but not what I asked for. I don't ever see the phrase"b^3-3a^2b+2a^3" in the set of equations. I asked for a complete derivation because I'm 100% certain whoever responds will asssume I know something that I don't know as in this case.

Thanks for trying but I simply cannot make that work here.

ps - Please don't mind my demeanor. I'm in a ton of pain and it makes me feel like poop. My concentration and patience is shot. I'm doing my best not to take it out on anybody.

jeffreyH · « **Reply #5 on:** 21/05/2018 12:23:15 »

I have corrected my post. I wrote it as a programmer would. Sorry.

PmbPhy · « **Reply #6 on:** 22/05/2018 19:43:25 »

Quote from: jeffreyH on 20/05/2018 22:30:42

b³-3a²b+2a³ = (b-a)²(2a+b) so that the factor of (b-a)² cancels.

That's all find and dandy but that can be gleaned from the paper I posted. That wasn't what I was asking help for. Here's the derivation. This was

Griffiths Probelm 1.7.jpg (291.98 kB . 1243x1580 - viewed 1865 times)

Bill S · « **Reply #7 on:** 22/05/2018 21:03:38 »

Pete, I don't know if NCTM could help.

https://www.nctm.org/mathforum/

PmbPhy · « **Reply #8 on:** 23/05/2018 02:11:37 »

Quote from: Bill S on 22/05/2018 21:03:38

Pete, I don't know if NCTM could help.

https://www.nctm.org/mathforum/

Hi Bill Many thanks but I already solved the problem. I was making one silly mistake afar another. Yikes!

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Need help with math problem

PmbPhy (OP)

Need help with math problem

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