1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Simultaneous equation question

  1. Oct 30, 2005 #1
    Hey just need my answer to be checked on this problem
    just to clarify x2 means x squared!

    Solve the following

    y = 2 - x
    x2 + 2xy = 3

    Substitute equations

    x2 + 2x(2 - x) = 3
    x2 + 4x - 2 x2 = 3
    -x2 + 4x - 3 = 0

    Factorising

    (-x + 1) (x - 3) = 0

    so x = -1 and 3
    _____________________________________________

    as y = 2 - x

    y = 2 - 3
    = -1

    y = 2 + 1
    = 3

    so the co ordinates for the two roots of this curve will be

    (-1, 3) and (3, -1)

    is this the right answer? i believe it to be, but my answer books says differently!

    Please check my answer.
    Thanx in advance!
     
  2. jcsd
  3. Oct 31, 2005 #2
    You made a small mistake where I highlighted.
     
  4. Oct 31, 2005 #3
    sorry, i still don't understand, i checked what i did, i can't see whats wrong with the bit highlighted!

    Can anyone elaborate?
     
  5. Oct 31, 2005 #4

    TD

    User Avatar
    Homework Helper

    I didn't read it all but if your factorization was correct, then x = 1 is a solution and not x = -1.
     
  6. Oct 31, 2005 #5
    i think i see what i have done wrong

    the x = 3 is right

    but it is -x = -1!

    so x = 1

    so to start again............

    as y = 2 - x
    y = 2 - 3
    = -1
    y = 2 - 1
    = 1
    so the co ordinates for the two roots of this curve is
    (-1, 3) and (1, 1)

    Thanx a lot, this is the answer in the book, easy mistake i made i think! bah humbug with the positive and negative signs!!

    Cheers! I can sleep now!
     
  7. Oct 31, 2005 #6

    TD

    User Avatar
    Homework Helper

    Good :smile:
     
  8. Nov 1, 2005 #7

    verty

    User Avatar
    Homework Helper

    A word of advice, when you factorise like that it usually helps to have the x^2 coefficient be positive.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Simultaneous equation question
  1. Simultaneous Equations (Replies: 12)

  2. Simultaneous equations (Replies: 8)

  3. Simultaneous Equations (Replies: 21)

  4. Simultaneous equations (Replies: 11)

  5. Simultaneous equations (Replies: 7)

Loading...