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Homework Help: A linear Algebra Problem (3x3 Matrix)

  1. Jan 31, 2013 #1
    1. The problem statement, all variables and given/known data
    I want to proove the determinant of the following 3x3 matrix is 0.

    1 1 1

    tanA tanB tanC

    tan2A tan2B tan2C

    where A+B+C=2pi.

    2. Relevant equations

    Sorry I don't know how to type here so I show in the attachment.

    3. The attempt at a solution

    Sorry I have attempted but found no way closed to the solution.

    Attached Files:

    • f.gif
      File size:
      959 bytes
    Last edited: Jan 31, 2013
  2. jcsd
  3. Jan 31, 2013 #2


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    Science Advisor

    If you want to do it then you first have to attempt to do it and you have shown no attempt. Under "relevant equations" you might put something like
    [tex]\left|\begin{array}{ccc}a & b & c \\ d & e & f \\ g & h & i\end{array}\right|= a\left|\begin{array}{cc}e & f \\ h & i\end{array}\right|- b\left|\begin{array}{cc}d & f \\ g & i\end{array}\right|+ c\left|\begin{array}{cc}d & e \\ g & h\end{array}\right|[/tex]
    as well as some trig identities like
    [tex]tan(2A)= \frac{2tan(A)}{1+ tan^2(A)}[/tex]
    Last edited by a moderator: Jan 31, 2013
  4. Jan 31, 2013 #3
    Sorry it is my bad. Thanks!
    Last edited by a moderator: Jan 31, 2013
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