Results 1 to 3 of 3

Math Help - System of Linear Equation

  1. #1
    Newbie
    Joined
    Jul 2012
    From
    NZ
    Posts
    5

    System of Linear Equation

    To solve a system of 3 linear equations, a student splits it into 2 subsystems as follows:

    SYSTEM 1
    (1/2)x-5y=-20
    x-(4/5)y=6

    SYSTEM 2
    (3/5)x-2y=-4
    (1/2)x-5y=-20

    Solve both sub systems. and state what your solution (if one exists) tells you about the original system of 3 linear equations.

    I've tried solving the 1st one and the 2nd by using the elimination method..

    S1=
    (1/1/2)x-5.8=-14
    =(1/1/2)x=-14+5.8
    =(1/1/2)x=-8.2
    im stuck from this point..how do i get rid of the 1/1/2 so it ll just be x.

    S2=
    (1/2)x-5y=-20
    (3/5)x-2y=-4
    ===========
    1/1/10=7y=-24
    -7y=-25.1
    y=-25.1/7
    y=-3.5857

    is this correct for system 2?

    what will the solution tell me about the original system of 3 linear equations.?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,653
    Thanks
    1478

    Re: System of Linear Equation

    I don't understand what you've done with S1... You should just multiply the equation by 2 and then subtract the second equation from the first...

    \displaystyle \begin{align*} x - 10y &= -40 \\ x - \frac{4}{5}y &= 6  \\ \\ -\frac{46}{5}y &= -46 \\ y &= 5 \\ \\ x - 10(5) &= -40 \\ x - 50 &= -40 \\ x &= 10 \end{align*}
    Last edited by Prove It; August 1st 2012 at 09:12 PM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jul 2012
    From
    NZ
    Posts
    5

    Re: System of Linear Equation

    Quote Originally Posted by Prove It View Post
    I don't understand what you've done with S1... You should just multiply the equation by 2 and then subtract the second equation from the first...

    \displaystyle \begin{align*} x - 10y &= -40 \\ x - \frac{4}{5}y &= 6  \\ \\ -\frac{46}{5}y &= -46 \\ y &= 5 \\ \\ x - 10(5) &= -40 \\ x - 50 &= -40 \\ x &= 10 \end{align*}
    I was using the elimination method where i would add the two equations and solve until i get x and then substitute the x value..guess i messed up that part
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Linear equation system
    Posted in the Math Topics Forum
    Replies: 2
    Last Post: May 24th 2010, 11:18 AM
  2. non linear system of equation
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: October 11th 2009, 01:12 PM
  3. non-linear differential equation system
    Posted in the Differential Equations Forum
    Replies: 2
    Last Post: October 7th 2008, 12:09 AM
  4. Help solving linear equation system
    Posted in the Advanced Algebra Forum
    Replies: 2
    Last Post: August 20th 2008, 08:44 PM
  5. help on system linear equation
    Posted in the Pre-Calculus Forum
    Replies: 0
    Last Post: November 8th 2007, 08:43 AM

Search Tags


/mathhelpforum @mathhelpforum