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Help with this math prob please, test tomorrow!!

Discussion in 'Off Topic [BG]' started by bassist 4 life, Dec 13, 2006.

  1. Evaluate the determinant of :

    | -1 3 4 |
    | 0 5 1 |
    | 6 -2 3|

    The answer is -119. I just don't know how you get -119

    you can use either expression by minors or diagonals to solve it

    please help, i have a test tomorrow
  2. karrot-x

    karrot-x Banned

    Feb 21, 2004
    Omicron Persei 8
  3. jade


    Mar 8, 2002
    First row reduce it to get a column of | "number" 0 0 |, it'll make your life easier.

    | -1 3 4 |
    | 0 5 1 |
    | 0 16 27|

    You can find the determinant by cofactor, so you can use any row or any column to do this. Pick the first row since it has the most number of 0. Since -1 is the only number, the rest will be zeros (any number multipled by 0 is 0). Dont forgot the negatives, since -1 is at the (1,1) position on the grid we have to multiply the determinant by (-1)^(1+1) to make sure the sign it correct. Since (-1)^2 is 1 we dont have to worry about it.

    so make a new matrix..

    (-1) | 5 1 |
    | 16 27|

    find the determinant! (ad-bc)

    (-1)[(5)(27)-(16)(1)] = -119

    Does it help? Or have I just confused you? I just had my Linear algebra final yesterday. Good luck with yours!
  4. he's 14 and I cant help him with his math? Now I feel low... but after reading Jade's post I think I'm remembering a little... but still...
  5. 98dvl


    Jan 31, 2002
    Don't worry, you'll never use that stuff in real life anyway.
  6. karrot-x

    karrot-x Banned

    Feb 21, 2004
    Omicron Persei 8
    Unless your job depends on it.
  7. jade


    Mar 8, 2002
    Dorry worry, they have computers to do this stuff for us. :p
  8. karrot-x

    karrot-x Banned

    Feb 21, 2004
    Omicron Persei 8
    Unless the computer breaks.


  9. fishstix


    Feb 28, 2006
    Recopy the first two columns to the right side of the determinant. Then add the products of the diagonals from top left to bottom right. From that sum take away the sum of the products of the diagonals from bottom left to top right.

    | -1 3 4 |
    | 0 5 1 |
    | 0 5 1 |


    | -1 3 4 | -1 3
    | 0 5 1 | 0 5
    | 6 -2 3| 6 -2



    If you are only having to work up to a 3 by 3 det., you'll be fine with this method. My H.S. students in Alg. 2 only have to work through 3 by 3's and thus this explination is as far as we have to go. There are more powerful generalized methods out there but save those for Pre-calc and beyond.
    Good luck,
  10. Thanks for the help guys,

    btw I just learnt how to solve matrices in my calculator , this iwll make things a lot easier.
  11. My head hurts from reading this. Thanks guys!
  12. Brad Barker

    Brad Barker

    Apr 13, 2001
    berkeley, ca
    i had to solve for the determinant of a 3x3 matrix for my quantum mechanics final.

  13. Minger


    Mar 15, 2004
    Rochester, NY
    I'm currently in AP Statistics na dAP Calculus...and have never seen this before in my life :D
  14. Neb Maro

    Neb Maro I don't think, but I still am.

    Oct 20, 2006
    So. Cali
    I despise higher math. To think I have Algebra 2, Geometry, Calculus, and Physics to look forward to.
  15. Jeff Moote

    Jeff Moote Supporting Member

    Oct 11, 2001
    Beamsville, ON, Canada
    Well, then it's something to look forward to!
  16. 98dvl


    Jan 31, 2002
    Like I said... Real life != school
  17. karrot-x

    karrot-x Banned

    Feb 21, 2004
    Omicron Persei 8
    Unless ....


  18. just write -119 and pretend you did it.
  19. Poop-Loops

    Poop-Loops Banned

    Mar 3, 2006
    Auburn, Washington
    I didn't do 3x3 determinants till last spring. You must be really ahead of the curve... or whereever you live is really ahead of the curve.

    Or I don't know, but it's cool that you're learning that now.
  20. jade


    Mar 8, 2002
    I quite enjoyed this class the second time I took it. It's quite simple but it's using a whole new set of rules and terminology. It's all about terminology..

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