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Matrices math question homework

  1. Jun 3, 2006 #1
    determine the value of k for which the matrix

    (2 4 1)
    (k -1 2)
    (7 7 4) has no inverse

    apparantly the answer is k = 1 but I cant see how.

    I worked it out to be -3
  2. jcsd
  3. Jun 3, 2006 #2


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    Gold Member

    Can you show your work?

    I obtained an answer that isn't k=1, by the way. Are you sure you copied the matrix and/or the answer down correctly ?
    Last edited: Jun 3, 2006
  4. Jun 3, 2006 #3
    I agree that it is not one, but I don't agree with your answer of -3. Assuming that the matrix you gave is correct, look back at your working (preferably post what you have done) - I checked my result with my calculator, and found the matrix to be singular.
  5. Jun 4, 2006 #4
    see I just wanted to be sure whether the book was wrong or not as it says it is 1. I tried working out the determinant step by step and making it equal to 0 then solve for 'k' like an algebra equation
  6. Jun 4, 2006 #5
    I worked it out to be neither 1 nor -3, and double checked in matlab.

    rework and check your signs carefully.
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