Results 1 to 6 of 6

Math Help - Algebra Matrices

  1. #1
    Newbie
    Joined
    Feb 2011
    Posts
    4

    Algebra Matrices

    Find all solutions to the system of equations.

    1. 3x^2 + 4y = 17
    2x^2 + 5y = 2

    2. xy = 12
    y = x - 4

    Thanks in advance!
    Last edited by mr fantastic; February 15th 2011 at 01:47 PM. Reason: Deleted excess questions.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,236
    Thanks
    28
    No matrices needed, if anything it will just make life harder.

    Quote Originally Posted by play60 View Post
    3x^2 + 4y = 17
    2x^2 + 5y = 2
    mulitply the first equation through by 5 and the second through by 4, then eliminate y by subtracting.

    Quote Originally Posted by play60 View Post

    xy = 12
    y = x - 4

    \displaystyle xy = 12 \implies x(x-4) = 12 \implies x^2-4x-12 = 0 \implies (x=6)(x+2)=0
    Last edited by mr fantastic; February 15th 2011 at 01:47 PM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Feb 2011
    Posts
    4
    I apologize for posting more than 2 questions.

    I am working on problem 1.

    I multiplied the first equation by 5 and the second by 4. I now have:

    15 20 85
    8 20 8

    Is this correct thus far? If so, what is the next step. I know I am to subtract, but am unsure how to do so. Thanks in advance.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,325
    Thanks
    1296
    What? What happened to the variables, x and y? If you are trying to write these as matrices, that might not work- these are NOT linear equations.
    (Actually it will if you think of these as "linear" in x^2 and y, not x and y.)

    I think you mean
    15x^2+ 20y= 85 and
    8x^2+ 20y= 8
    Subtract the second equation from the first to get a single equation in x.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Feb 2011
    Posts
    4
    Thank you. Yes, that is what I intended.

    The answer to problem 1 (that I got) is: x = 11 and y = -4.

    The answer to problem 3 (that I got) is: x = -1, y = 0, z = 1

    I am struggling with problem 2. How do I set this problem up?

    For problem 4, do I use Gaussian elimination or Gauss-Jordan elimination?

    Thanks again!
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,325
    Thanks
    1296
    Once again, these are NOT linear equations- "Gaussian Elimination might not work. For #2, the simplest thing to do is to use the second equation, y= x- 4 to replace the "y" in the first equation:
    xy= x(x- 4)= 12. That's a quadratic equation for x.

    I see no third or fourth equations. I suspect a moderator has removed them since more than two questions in a post is against the rules. If you have more questions, open a new thread.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Linear algebra with matrices
    Posted in the Advanced Algebra Forum
    Replies: 3
    Last Post: April 7th 2010, 03:36 AM
  2. Transformation using matrices (algebra help)
    Posted in the Algebra Forum
    Replies: 2
    Last Post: May 9th 2009, 12:35 AM
  3. the algebra of Diagonalized matrices
    Posted in the Advanced Algebra Forum
    Replies: 5
    Last Post: January 26th 2009, 11:51 AM
  4. Linear algebra Matrices
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: September 13th 2008, 07:08 PM
  5. Linear algebra matrices
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: September 13th 2008, 06:52 PM

Search Tags


/mathhelpforum @mathhelpforum