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Math Help - Find x and y so A^2 = A

  1. #1
    Member mybrohshi5's Avatar
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    Find x and y so A^2 = A

    If A = x 4
    .........y 7

    (^^^^ that is a 2x2 matrix)

    determine the values of x and y for which A^2=A.


    No idea how to start this one.

    i didnt think it was possible because

    A^2 = x^2 16
    ..........y^2 49

    A = x 4
    ......y 7

    so how can A^2 ever equal A because no matter what the x and y values are, 4 and 7 will never equal 16 and 49?

    Help please

    Thank you
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  2. #2
    Flow Master
    mr fantastic's Avatar
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    Quote Originally Posted by mybrohshi5 View Post
    If A = x 4
    .........y 7

    (^^^^ that is a 2x2 matrix)

    determine the values of x and y for which A^2=A.


    No idea how to start this one.

    i didnt think it was possible because

    A^2 = x^2 16
    ..........y^2 49

    A = x 4
    ......y 7

    so how can A^2 ever equal A because no matter what the x and y values are, 4 and 7 will never equal 16 and 49?

    Help please

    Thank you
    The first thing you should do is review how to multiply matrices. Because A^2 is NOT equal to what you got. Note: A^2 = A \times A.
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  3. #3
    Member mybrohshi5's Avatar
    Joined
    Sep 2009
    Posts
    230
    Duh haha thank you. its getting late here and i shouldnt be doing math when im tired. i always forget little things like that.

    thank you again.
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