Results 1 to 9 of 9

Math Help - Not solvable system of linear equations in Mathematica

  1. #1
    Member
    Joined
    Mar 2010
    Posts
    96

    Not solvable system of linear equations in Mathematica

    How can I find $t$ for system of linear equations, that the system would not be solvable?

    I tryed with this code:

    Code:
    x = 10
    y = 10
    z = 10
    Solve[{ 9 x - 8 y + t*z == 1, 6 x - 8 y - 5 z == 1,  3 x  -7 y + 9 z == 1}, {t}]
    Follow Math Help Forum on Facebook and Google+

  2. #2
    A Plied Mathematician
    Joined
    Jun 2010
    From
    CT, USA
    Posts
    6,318
    Thanks
    5
    Awards
    2
    You have a highly over-determined system there. There are no solutions. Think about it:

    90-80+10t=1
    60-80-50=1
    30-70+90=1

    Some of those equations are downright incorrect. I would review your steps for arriving at that system of equations. What's the bigger context for this problem?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Mar 2010
    Posts
    96
    Sorry, forget x,y,z values.

    I need to find t to be not solvable. For t = 1, it's solvable, for t = 2 it's solvable and so on...
    but when it's not?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    A Plied Mathematician
    Joined
    Jun 2010
    From
    CT, USA
    Posts
    6,318
    Thanks
    5
    Awards
    2
    Ok. Try setting

    \left|\begin{matrix}9&-8&t\\6&-8&-5\\3&-7&9\end{matrix}\right|=0.

    That's a determinant there. What do you get?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    A Plied Mathematician
    Joined
    Jun 2010
    From
    CT, USA
    Posts
    6,318
    Thanks
    5
    Awards
    2
    Whoops. That approach won't work. Take a look at this thread. Make sure you scroll all the way down to the end to get the real reason why that works.
    Last edited by Ackbeet; November 5th 2010 at 11:04 AM. Reason: Justification.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Member
    Joined
    Mar 2010
    Posts
    96
    I get a solution. Great.

    It works, your approach works.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    A Plied Mathematician
    Joined
    Jun 2010
    From
    CT, USA
    Posts
    6,318
    Thanks
    5
    Awards
    2
    Wonderful. What is your value for t?
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Member
    Joined
    Mar 2010
    Posts
    96
    -(137/6)
    Follow Math Help Forum on Facebook and Google+

  9. #9
    A Plied Mathematician
    Joined
    Jun 2010
    From
    CT, USA
    Posts
    6,318
    Thanks
    5
    Awards
    2
    That is correct.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. 2x2 system of linear equations
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: September 24th 2011, 04:02 AM
  2. System of linear equations.
    Posted in the Algebra Forum
    Replies: 5
    Last Post: August 10th 2010, 12:03 AM
  3. Replies: 2
    Last Post: April 20th 2010, 04:26 PM
  4. System of linear equations
    Posted in the Algebra Forum
    Replies: 5
    Last Post: November 12th 2009, 08:03 AM
  5. System of Linear Equations
    Posted in the Algebra Forum
    Replies: 2
    Last Post: February 26th 2009, 10:44 PM

Search Tags


/mathhelpforum @mathhelpforum