Results 1 to 3 of 3

Math Help - Values of K that makes a matrix non-invertible

  1. #1
    Newbie
    Joined
    Sep 2009
    Posts
    11

    Values of K that makes a matrix non-invertible

    I have a 3x3 matrix:

    1, -2, 0
    k, 1, k
    0, -2, 1

    and I have to find all values of K that make the matrix non-invertible. I know matrices are non-invertible when 2 rows are proportionate, but (in my mind) this won't work in the matrix given because no 2 rows will be proportionate for a single k value. This answer is however marked incorrect when input in WileyPlus (online math questions thing).

    If anyone has insight into if there is actually an answer and I'm missing it or can provide more insight that would be great!

    cheers
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,663
    Thanks
    298
    Awards
    1
    A matrix is non-invertable, or singular, when its determinant is zero.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Apr 2005
    Posts
    14,973
    Thanks
    1121
    Quote Originally Posted by Landyach View Post
    I have a 3x3 matrix:

    1, -2, 0
    k, 1, k
    0, -2, 1

    and I have to find all values of K that make the matrix non-invertible. I know matrices are non-invertible when 2 rows are proportionate, but (in my mind) this won't work in the matrix given because no 2 rows will be proportionate for a single k value. This answer is however marked incorrect when input in WileyPlus (online math questions thing).
    Yes, it is true that "if two rows of a matrix are proportionate then the matrix is not invertible". Your error is in thinking that the converse of that, "if a matrix is not invertible, then two rows are proportionate" must be true. It isn't.

    If anyone has insight into if there is actually an answer and I'm missing it or can provide more insight that would be great!

    cheers
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. What makes this matrix true?
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: April 26th 2010, 04:44 PM
  2. For what values is the matrix invertible?
    Posted in the Advanced Algebra Forum
    Replies: 3
    Last Post: September 29th 2009, 11:57 PM
  3. Get just a few values of invertible matrix
    Posted in the Advanced Algebra Forum
    Replies: 2
    Last Post: December 10th 2008, 01:59 PM
  4. Replies: 3
    Last Post: October 14th 2008, 11:45 PM
  5. Replies: 3
    Last Post: June 15th 2008, 06:08 AM

Search Tags


/mathhelpforum @mathhelpforum