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LINEAR ALGEBRA help!

  1. Sep 10, 2008 #1
    LINEAR ALGEBRA... URGENT... help!

    1. The problem statement, all variables and given/known data

    Solve the System...

    [1,0,0,-7,8] That is a 3x5 matrix.
    [0,1,0,3,2,]
    [0,0,1,1,-5]


    2. Relevant equations
    ...


    3. The attempt at a solution

    I dont know why this is so hard to me, ive literally tried for about 2 hours to solve this. Calc 1-4 came naturally to me, but this is giving me so much trouble. Id be more happy right now with someone telling me the best way to approach these problems than a hint at this specific answer. Whenever i try to eliminate one variable, another one comes into the row and i am stuck with 2 variables, so i cant solve for any of the variables... please someone give me some advice on the best way to solve these... im dying over here
     
  2. jcsd
  3. Sep 10, 2008 #2

    Dick

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    Re: LINEAR ALGEBRA... URGENT... help!

    If you have 5 variables and 3 equations you will definitely be left with at least 2 undetermined variables. There's nothing you can do about that. The answer will have to be expressed in terms of those two variables, i.e. x=s+t, y=s-t, z=2t, s=s and t=t.
     
  4. Sep 10, 2008 #3
    Re: LINEAR ALGEBRA... URGENT... help!


    Actually, 4 variables, i forgot to put the line before the last row, so i assume you can solve for 4 unknowns with only 3 equations? and if so, finally, THANK YOU DICK! this problem has been killing me for the past 2 hours, i knew something was up with it... thank you for verifying it!!!!!!!!!!!!!!!!!
     
  5. Sep 10, 2008 #4

    Dick

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    Re: LINEAR ALGEBRA... URGENT... help!

    4 unknowns with 3 equations leaves you with at least one undetermined value. Looking at your equations I can tell you it's exactly one. If you are getting two, that might be a problem.
     
  6. Sep 10, 2008 #5
    Re: LINEAR ALGEBRA... URGENT... help!

    Wow, this is embarassing haha. That is how i originally did the problem and got the correct equations... when i went to the back of the book to check i saw a matrix with actual numbers in it... i was looking at chapter 1.1 not 1.2 (which we are currently on) so i assumed my answers were wrong... when i went back and looked at 1.2, i was right from the get go... well anyway, thanks once again dick for the help!
     
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