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Homework Help: Question on homogeneous linear systems

  1. Sep 5, 2005 #1

    mpm

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    I have a homework question that I dont really understand what they are asking.

    The book I am using is terrible so I was hoping someone could shed some light.

    Question:

    Give a geometric explanation of why a homogeneous linear system consisting of two equations in three unknowns must have infinitely many solutions. What are the possible numbers of solutions for a nonhomogeneous 2 x 3 linear system? Give a geometric explanation of your answer.

    If anyone could help me on this I would appreciate it.

    mpm
     
  2. jcsd
  3. Sep 5, 2005 #2
    2 equations in 3 unknown must have infinitely many solutions, because the only way you could have one singular solution is to have 3 equations for each unknown...
    i think that there's some matrix(or is it determinant?) formula (i forgot what it's called, because it's been a long time since i've touched that...) that you can you use to prove...
     
    Last edited: Sep 6, 2005
  4. Sep 5, 2005 #3
    or you could draw pictures of the planes in space, and find out that there are infinitely many solutions...
     
  5. Sep 5, 2005 #4
    Well let's say you reduce it to the form:

    [tex]\left[\begin{array}{ccc|c}1 & 0 & a & 0 \\ 0 & 1 & b & 0\end{array}\right][/tex]

    The general solution is then:

    [tex]x_3\begin{bmatrix}-a \\ -b \\ 1\end{bmatrix}[/tex]

    ...which has a solution for each value of [itex]x_3[/itex].
     
  6. Sep 5, 2005 #5

    mpm

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    Ok I think I understand the homogeneous part of the question. Can anyone help on the nonhomogeneous part?
     
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