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Homework Help: Lin. Algebra: Find coordinates on a, b, c, d such that AB=BA

  1. Mar 22, 2015 #1
    1. The problem statement, all variables and given/known data

    Matrix A =

    1 1
    0 1

    Matrix B =

    a b
    c d

    Find coordinates on a, b, c, d such that AB = BA.

    2. Relevant equations

    3. The attempt at a solution

    I calculated AB and BA with simple matrix multiplication, but am not sure where to go from here.

    AB =

    a + c a + b
    c | d

    BA =

    a | a + b
    c | c + d
  2. jcsd
  3. Mar 22, 2015 #2


    Staff: Mentor

    Assuming your work so far is correct (I didn't check), set the elements of AB equal to those of BA. This will give you four equations in your four variables.
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