Results 1 to 2 of 2

Math Help - simultaneous linear equations

  1. #1
    Member smmmc's Avatar
    Joined
    Jan 2009
    From
    House
    Posts
    80

    simultaneous linear equations

    hi
    q1- The system of equations y = x^2 − 4x + c and y = −7x + 8 has two solutions, one at
    x = 1, and another at x = −4. Find the value of c.

    i made the 2 equations equal to each other so
    x^2 − 4x + c= −7x + 8
    so rearrange
    x^2 + 3x -8 +c
    sub x=-1 in
    so it would be c=4 but then i thought to factorise the equation and use null factor law to find c?

    thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by smmmc View Post
    hi
    q1- The system of equations y = x^2 − 4x + c and y = −7x + 8 has two solutions, one at
    x = 1, and another at x = −4. Find the value of c.

    i made the 2 equations equal to each other so
    x^2 − 4x + c= −7x + 8
    so rearrange
    x^2 + 3x -8 +c
    sub x=-1 in
    so it would be c=4 but then i thought to factorise the equation and use null factor law to find c? Mr F says: Why would you do that? Substitute x = 1 => c = 4. Substitute x = -4 => c = 4. Solved.

    thanks
    ..
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Simultaneous non-linear equations.
    Posted in the Algebra Forum
    Replies: 5
    Last Post: September 19th 2011, 11:23 AM
  2. Replies: 3
    Last Post: February 27th 2009, 07:05 PM
  3. Simultaneous Linear Equations help.
    Posted in the Algebra Forum
    Replies: 2
    Last Post: January 28th 2009, 03:13 PM
  4. Two Simultaneous linear equations
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: December 11th 2008, 10:20 AM
  5. Simultaneous linear equations
    Posted in the Algebra Forum
    Replies: 6
    Last Post: November 17th 2008, 11:58 AM

Search Tags


/mathhelpforum @mathhelpforum