Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes-Benz Forum > General Discussions > Off-Topic Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 07-14-2011, 02:48 PM
TheDon's Avatar
Open Discussion Moderator
 
Join Date: Oct 2005
Posts: 13,212
discrete math help

I need some help from our resident math genius posters. I am working on my discrete stuff and I need help with the following problem

find the gcd of a = -1575 and b = 231, write it in the form alphaX + betab, where alpha , B belong to Z.

we were taught a method like this

-1575 1 0
231 0 1

then find q ( a/b floored if b>o and take the ceiling if b<0)
then r which is : a-qb

and then that makes the next row with the numbers under the 0 and 1 are found by such (1-q(0), and 0-q(1)... the 1 in the first part is from the first row second column and the zero is from the second row second column) Then same idea for the next number. and that method is used down the line.

its hard to explain I guess... I need to do good on this homework so it helps my grade. If anything I can scan in the sheet.
Reply With Quote
  #2  
Old 07-14-2011, 02:57 PM
TheDon's Avatar
Open Discussion Moderator
 
Join Date: Oct 2005
Posts: 13,212
if you know what I am talking about let me know what you get. I just worked through it slowly, double checking my method and I got, in the proper form

gcd(-1575,231) = -21 = 5(-1575)+34(231)

5(-1575)+34(231) = -21

so I guess it checks out?
Reply With Quote
  #3  
Old 07-14-2011, 04:27 PM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
certainly not a math genius... but what is the name of the process you are supposed to be learning (ie.. chapter name etc..)? There are a few ways to do this.

Perhaps you can teach us... thats the best way to learn.
__________________

Reply With Quote
  #4  
Old 07-14-2011, 05:14 PM
Registered User
 
Join Date: Sep 2001
Location: central Texas
Posts: 17,277
Anytime you are writing anything and are going to use abbreviations you need to spell out what that is the first time ... then you can use the shortened version and people will know what you are referring to..
Not just here... but that is standard practice in English for all writing.
Reply With Quote
  #5  
Old 07-14-2011, 07:13 PM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
I got the same using Euclid. Nice job.
__________________

Reply With Quote
  #6  
Old 07-14-2011, 08:31 PM
Yak Yak is offline
Registered User
 
Join Date: Aug 2009
Location: San Antonio, TX
Posts: 1,711
Can GCD's be negative?
Reply With Quote
  #7  
Old 07-14-2011, 09:46 PM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
Quote:
Originally Posted by Yak View Post
Can GCD's be negative?

good catch, buddy.

it shouldn't be.

OP: in the first step, take a -1 out of -1575 to make it (-1)1575 and bring that over so that you get 1575=6*231+189 and carry it through your work.

you could just switch the signs at the end, but it depends on your teacher and how you see it.

21=-5(-1575)-34(231)
__________________

Reply With Quote
  #8  
Old 07-14-2011, 11:10 PM
TheDon's Avatar
Open Discussion Moderator
 
Join Date: Oct 2005
Posts: 13,212
Euclids method is one way then we learned this other way which I have no idea of the name. But apparently I did it correctly.
Reply With Quote
  #9  
Old 07-14-2011, 11:11 PM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
Are you row-reducing or using a determinant?

You saw Yak's post right?
__________________

Reply With Quote
  #10  
Old 07-14-2011, 11:14 PM
Registered User
 
Join Date: Sep 2001
Location: central Texas
Posts: 17,277
Someone needs to share with the lower math people what yall are talking about...
Reply With Quote
  #11  
Old 07-14-2011, 11:34 PM
Yak Yak is offline
Registered User
 
Join Date: Aug 2009
Location: San Antonio, TX
Posts: 1,711
GCD = greatest common denominator.

21 is the largest number that goes into both 1575 (or -1575) and 231.

There are different methods. Euclidean and Matrix are two.

If the teacher expects a linear equation, then your coefficients (alpha and beta) may have the wrong sign and you won't get max points.

I'd review your notes or examples and see if there's anything about "ignore the minus sign".
Reply With Quote
  #12  
Old 07-14-2011, 11:44 PM
Registered User
 
Join Date: Sep 2001
Location: central Texas
Posts: 17,277
I thought that was ' Great Carbon Diode '....
so we are just talking finding largest common factors ?
Reply With Quote
  #13  
Old 07-15-2011, 07:22 AM
Admiral-Third World Fleet
 
Join Date: Feb 2002
Location: Central FL
Posts: 3,068
Quote:
Someone needs to share with the lower math people what yall are talking about...
I disagree. WGAS at our advanced ages. Art history, music, language, I can see, but math? I am checking out of this one....
__________________
80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)
Reply With Quote
  #14  
Old 07-15-2011, 10:01 AM
TheDon's Avatar
Open Discussion Moderator
 
Join Date: Oct 2005
Posts: 13,212
Quote:
Originally Posted by jt20 View Post
Are you row-reducing or using a determinant?

You saw Yak's post right?
Maybe row reducing. With negative number it was not an issue since it did work out. Maybe I'll scan inmy work later and show you all.
Reply With Quote
  #15  
Old 07-16-2011, 10:06 AM
TheDon's Avatar
Open Discussion Moderator
 
Join Date: Oct 2005
Posts: 13,212
Here is another one for you all

Prove that the equation 3X ≡ 1 mod 6 has no solutions.

so far I have it solved for x which is x = 2k - 1/3 and then I am stuck

I honestly need help with all of it. I have posted a screen cap of the page this is on.

page 1


page 2

Last edited by TheDon; 07-16-2011 at 10:33 AM.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

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 On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 05:29 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page