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Math Help - Finding The Determinant

  1. #1
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    Finding The Determinant

    I need to find the determinant of the matrix

    2 -1 3
    1 4 -2
    -1 0 1

    by the 3rd row.


    I ended up getting -1(2-12) - 1(8+1) = 10 - 9 = 1

    Is this correct?
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by TreeMoney View Post
    I need to find the determinant of the matrix

    2 -1 3
    1 4 -2
    -1 0 1

    by the 3rd row.


    I ended up getting -1(2-12) - 1(8+1) = 10 - 9 = 1

    Is this correct?
    Where did the -sign in front of 1(8+1) come from? (or to put it another
    way it should be +).

    You could check this yourself by expanding by the first row.

    RonL
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  3. #3
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    when i did expanded by the first row, i got 17.

    2(4) -1(3) + 3(4) = 8 - 3 + 12 = 17.

    Does it make a difference if you expand by a different row? because the problem says to expand by the 3rd row. When i did it again I ended up getting -1. I don't get it.
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by TreeMoney View Post
    when i did expanded by the first row, i got 17.

    2(4) -1(3) + 3(4) = 8 - 3 + 12 = 17.

    Does it make a difference if you expand by a different row? because the problem says to expand by the 3rd row. When i did it again I ended up getting -1. I don't get it.
    No it should be the same however you expand it, When I expand by the
    first row I get:

    2(4) - (-1)(1-2)+3(4) = 8 - 1 +12 =19.

    When I expand about the last row I get:

    -1(2-12) - 0(4-3) + 1(8+1) = 10 + 9 = 19

    RonL
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  5. #5
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    I figured out what i was missing. The negative sign in front of the first 1 in the last row. I must have missed it when i was copying things over. Thanks!!!!!
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