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Math Help - Check my proof

  1. #1
    Junior Member
    Joined
    Apr 2008
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    Check my proof

    A and B are n x n orthogonal matricies...show that

    A(A^t+B^t)B=A+B

    Where A^t and B^t are the transposes of A and B

    Here is my working:

    LHS= A(A^t+B^t)B
    = (A*A^t+A*B^t)B
    = (I+A*B^t)B
    = IB+A*B^t*B
    = B+A*I
    = A+B

    I know I have solved it correct and all..i jsut need some solid comfirmation..thats all thanks.
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  2. #2
    Lord of certain Rings
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    IISc, Bangalore
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    Quote Originally Posted by deragon999 View Post
    A and B are n x n orthogonal matricies...show that

    A(A^t+B^t)B=A+B

    Where A^t and B^t are the transposes of A and B

    Here is my working:

    LHS= A(A^t+B^t)B
    = (A*A^t+A*B^t)B
    = (I+A*B^t)B
    = IB+A*B^t*B
    = B+A*I
    = A+B

    I know I have solved it correct and all..i jsut need some solid comfirmation..thats all thanks.
    Nice
    It is correct
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  3. #3
    Junior Member
    Joined
    Apr 2008
    Posts
    72

    Thanks

    Thanks..have been on holiday for 2 weeks so stuff was more difficult...
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