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Homework Help: Proof of y-intercept

  1. Jun 8, 2010 #1
    1. The problem statement, all variables and given/known data

    Prove or Disprove: In the equation y=mx+b, b is the y-intercept.

    3. The attempt at a solution

    I know that this statement is true, and i know that to prove anything im suppossed to use a formula, not give examples. but how should i go about doing this if the formula is the question?
  2. jcsd
  3. Jun 8, 2010 #2


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    At any point on the y-axis, what is the x-coordinate?
  4. Jun 11, 2010 #3
    The y intercept occurs when x = 0 right.... that is the definition of the y intercept. Thus:

    y = 0x + b... y = b
    There is no real other way to prove this that isnt just being really obvious...
  5. Jun 11, 2010 #4


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    It seems to prove it to me. Even though it's obviously simple, it still does the job it's meant to.

    For another "slightly" more complicated one, prove the y-intercept for the line ax+by+c=0 is always -c/b, where [itex]b\neq 0[/itex]. This is basically the same thing, just a bit more complicated since it wouldn't usually be done in 1 simple step. Getting to quadratics complicates things more-so.
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