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Homework Help: Determine whether the equation represents y as a function of x

  1. Oct 7, 2009 #1
    1. X^2 + y = 8

    2. Relevant equations

    3. my steps:
    y = 8 - x^2
    x^2 = 8 - y

    (8-y) + y = 8

    Not a function.
    My logic is, because the equation does not equal y, it is not a function

    Please show me step by step the right answer, and preferably the reason why.
  2. jcsd
  3. Oct 7, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    You already had it in the first step. And it just gets crazy after that. If you don't know why, I think you should look up the definition of 'function' and tell us what it is.
  4. Oct 7, 2009 #3
    Oh. It's not a function because y = -x^2 + 8 ?
  5. Oct 7, 2009 #4
    Please assist me in my retardation. :( It is immensely painful.
  6. Oct 7, 2009 #5


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    Science Advisor
    Homework Helper

    Exactly wrong. y IS a function of x because y=(-x^2)+8. I'm going to ask you once more to look up the definition of a 'function'. Post it here for further discussion.
  7. Oct 8, 2009 #6


    Staff: Mentor

    The two equations above are equivalent to the one you started with, but as Dick already said, you had what you need in the first one above, and the one after that is just wasted motion.
    Now this one is always true, but is completely unrelated to the equation you started with and the two above.
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