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Homework Help: Find the determinant of a matrix

  1. Jan 1, 2007 #1
    Bonsoir everyone

    can anyone confirm if i got the answer right or wrong:

    Question:

    find the determinant of A. A is a matrix and is equal to

    1 5 -3
    3 -3 3
    2 13 -7

    (i think you've already guessed that i don't have latex)

    My answer:

    i got -18


    I would be grateful if anyone could confirm my answer, and if it's wrong i'll write out all the steps that i did in order to get that answer

    Merci :smile:
     
  2. jcsd
  3. Jan 1, 2007 #2
    Did you use ninja math or cofactors? I like ninja math:

    [(1*-3*-7)+(5*3*2)+(3*13*-3)]-[(-3*-3*2)+(3*13*1)+(5*3*7)]=? <----- Is that -18?
     
  4. Jan 1, 2007 #3
    You're correct.
     
  5. Jan 1, 2007 #4
    According to my TI-83, thats it
     
  6. Jan 1, 2007 #5
    Thank you all so much!...(i knew i was right ;) )

    and you could help me further by telling me how to find det(B^3) where det B= 4

    i don't think that it's as simple as 4^3...is it?
     
  7. Jan 1, 2007 #6
    ninja math?
     
  8. Jan 1, 2007 #7

    matt grime

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    Det is multiplicative (Det(XY)=Det(X)Det(Y)). You have been taught this. So use it.
     
  9. Jan 1, 2007 #8
    so it is 4^3, and my answer is 64
     
  10. Jan 1, 2007 #9
    Ninja math, basketweave, whatever you want to call it. You slice along the diagonals. So if you have matrix A, you would do

    (A11*A22*A33+A12*A23*A31+A21*A32*A13)-(A13*A22*A31+A12*A21*A33+A23*A32*A11)
     
  11. Jan 1, 2007 #10

    radou

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    That 'Ninja math' method is also called the Sarus rule, and it only applies for determinants of matrices of order 3.
     
  12. Jan 1, 2007 #11
    Yes I forgot to mention it is only for 3x3. Sarus rule? I did not know that. I prefer ninja math other Sarus rule though.
     
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