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Math Help - Please Help. A and Adj A with missing entries

  1. #1
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    1

    Please Help. A and Adj A with missing entries

    The question is Asking to find A And Adj A when we have both with some missing entries.

    A =
    2 1 4
    3 / /
    1 / /

    Adj A =
    / / -1
    / 8 /
    / 3 1

    First Column is empty in Adj A.

    The questions asks to find A and Adj a by finding the missing entries which i denoted here by using the symbol ( / )

    Please help
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  2. #2
    Banned
    Joined
    Oct 2009
    Posts
    4,261
    Quote Originally Posted by rodanader View Post
    The question is Asking to find A And Adj A when we have both with some missing entries.

    A =
    2 1 4
    3 / /
    1 / /

    Adj A =
    / / -1
    / 8 /
    / 3 1

    First Column is empty in Adj A.

    The questions asks to find A and Adj a by finding the missing entries which i denoted here by using the symbol ( / )

    Please help

    For example look at the 2-2 entry in Adj \,A , which is 8: this entry is the determinant of the minor A_{22} of the original matrix, i.e.: "erase" the second row and

    the second column of A and calculate the determinant of the remaining 2x2 matrix: we get A_{22}=\det\begin{pmatrix}2&4\\1&x\end{pmatrix} \Longrightarrow 8=2x-4\Longrightarrow x=6 and we've found

    the entry 3-3 of A.

    Continue as above with other entries.

    Tonio
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