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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


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    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.
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