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!

Finding intersections

  1. Sep 27, 2004 #1
    i need some help with the following:

    i know how to calculate the intersections when an equation like 3x+4y=33, y=x-1. but what do i do when y=x-1 becomes 2y=x-1; all of this using the substitution method. thnx
  2. jcsd
  3. Sep 27, 2004 #2
    If 2y = x - 1 then y = (x - 1)/2 = 0.5x - 0.5.
  4. Sep 27, 2004 #3
    thts what thought but it doesnt seem to correlate with the answers in the textbook. i'll try again. thnx all the same
  5. Sep 27, 2004 #4


    User Avatar

    There are two simple ways to substitute.

    First, you can add 1 to both sides of the second equation:
    2y + 1 = x - 1 + 1
    2y + 1 = x
    So now you can substitute 2y+1 instead of x in the first equation.

    Another way would be to multiply both sides with 1/2:
    2y * 1/2 = (x - 1) * 1/2
    y = (x-1)/2
    Now you can substitute (x-1)/2 instead of y.

    Remember, you are allowed to add the same number to both sides, and to multiply both sides with the same number.
  6. Sep 27, 2004 #5
    i jus thought tht it wud be a little bit more complicated, but thnx all the same, jus needed to make sure i was on the right track.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook