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Matrix multiplication

  1. Nov 7, 2009 #1
    1. The problem statement, all variables and given/known data
    Find A*B^T, where A=

    2 1
    5 3

    And B=

    1 -1 1
    -1 1 1

    2. Relevant equations


    3. The attempt at a solution

    The problem is, is that if I get the transpose of B, I will end up with a 3x2 matrix. Isn't this impossible to multiply by a 2x2 matrix? Maybe the answers is just 'not possible', but I have a feeling I'm doing something wrong. Anybody got any pointers? Thanks!
  2. jcsd
  3. Nov 7, 2009 #2


    User Avatar
    Homework Helper

    You are right, A*BT can't be computed. (AB)T can though, are you sure you weren't supposed to calculate that?
  4. Nov 7, 2009 #3
    The way it was actually written was BTA, so I think it made a point of showing that it wasn't (AB)T. So I'm thinking that the answer is that it can't be computed? Thanks for the quick reply!

    EDIT: ooooooooooh. Ooops. How embarassing. Of course it makes a difference when B comes first. Argh!
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