Results 1 to 5 of 5

Math Help - 2 by 2 gaussian elimination help...wtf is this q asking?

  1. #1
    Newbie
    Joined
    Mar 2009
    Posts
    15

    Unhappy 2 by 2 gaussian elimination help...wtf is this q asking?

    Is this a possible gaussian elimination. It is asked in a genuine question for gaussian elimination btw.

    2x + 3y = 5
    6x + 9y = 15

    As a matrix it looks like

    2 3 |5
    6 9 |15

    But when you do: row 2- 3*row 1
    you get 0 0 0 in the bottom row and now way of working out the x & y values......am i missing something here?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,686
    Thanks
    617
    Hello, Latkan!

    Your work is correct.

    If you get a row of zeros (all the way across), there is an infinite number of solutions.

    Look again and you'll see that the two given equations are equivalent.
    The second equation is merely 3 times the first.
    (They gave us the same equation twice!)
    There's not enough information for a unique solution.

    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Mar 2009
    Posts
    15
    ahh yes i thought as much however another question is asking a similar thing but this time both the x and y values are equal to 0 but the answer is not zero:

    2x + 3y = 1
    6x + 9y = 5

    as you can see

    2 3 | 1
    6 9 | 5

    row 2- 2*row 1 = 0 0 3

    so 0x + 0y = 3???? this cannot be true. So does this mean that the second row is null and tht there are an infinite number of solutions again?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Member
    Joined
    Oct 2009
    Posts
    218
    If you get something like "0x + 0y = 3" then that means that there are no solutions.

    But I think you meant row 2- 3*row 1 = 0 0 2
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Mar 2009
    Posts
    15
    thnx i realised it was a no solution once i looked over my workings.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: September 12th 2011, 09:03 PM
  2. [SOLVED] Gaussian elimination help II
    Posted in the Advanced Algebra Forum
    Replies: 2
    Last Post: June 28th 2011, 06:27 PM
  3. Replies: 1
    Last Post: February 16th 2011, 02:06 PM
  4. Gaussian elimination.
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: October 12th 2010, 05:06 AM
  5. Gaussian Elimination
    Posted in the Calculus Forum
    Replies: 1
    Last Post: June 3rd 2009, 06:06 PM

Search Tags


/mathhelpforum @mathhelpforum