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Unit of the Determinant of a 2-space Matrix

  1. May 12, 2007 #1
    Do determinants of a 2-space matrix have a unit of [units]^2?
    Also, does A_parallelogram = || u x v|| have a unit of [units]^2 too?
    This has confused me as Area has a unit of [units]^ 2 but the examples from the Contemporary Linear Algebra (Anton and Busby) text book does not state any units at all.
     
  2. jcsd
  3. May 12, 2007 #2

    HallsofIvy

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    The area of a parallelogram has units of "u2" where u is whatever unit is being used to measure area. That is a specific application of norm and does NOT say that norm of the cross product of a vector has any units at all! Are you assuming that there is some form of "measurement" so that the vectors in whatever vector space you are talking about have a specific unit? And that raises the question, are you thinking of some specific vector space?
     
  4. May 12, 2007 #3
    Well, yeah. Finding the area of a unit square 'ABCD' that is represented by a 2x4 M matrix =
    [ 0 1 1 0 ]
    [ 1 1 0 0 ]
    which has been multiplied by a 2x2 matrix N =
    [ -2 0 ]
    [ 0 -2 ]

    I had to calculate the area of N.M and the determinant of the N matrix.
    And I was just wondering since it's the area (found by Aparallelogram = || u x v||) do I just write [units]^2?
    Also since I'm meant to find out that the determinant is the area of the parallelogram, should I write [units]^2 or leave it blank?

    -- So there is an application of the norm of the cross product of two adjacent vectors in 2-space (Aparallelogram = || u x v||), in this situation should I put [units]^2 in the answer? I deduce that I'm not meant to know about det(N) being the area of N.M so I guess I won't write any units for that.
     
    Last edited: May 12, 2007
  5. May 12, 2007 #4

    HallsofIvy

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    What units are you told the length is measured in? If you are not given any measurements for a length, then I would not write any units for the area.
     
  6. May 12, 2007 #5
    No units, it just says calculate the area of N.M and calculate det(N).
    I just want to cover my bases as it asked for area and I thought I should just put a unit of 'units^2' at the end...
     
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