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Relations And Functions?

  1. May 6, 2004 #1
    How do you...

    Draw the graph of y=3x-2 on the grid. Identify at least two points on the graph by their coordinate pairs.

    Anybody get that??

    It's one of those x,y axis grid thingers. And theres a table under it with 8 columns and 2 rows. Kinda like..
    ______________________________________
    X | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
    Y | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |


    Something like that. Anybody help???
     
  2. jcsd
  3. May 6, 2004 #2
    Also, I am asked to pick out which table represents a relation that is NOT a function.

    A.
    Input Value | +9 | 4 | 16 | 32
    Output value|-18 | 8 | 32 | 64

    B.
    Input Value | 0 |1/-1|2/-2| 3
    Output value| 0 | + 1 | +2 | 9

    C.
    Input Value | -2 | -1 | 0 | 1
    Output value| +4 | +2 | 0| -2

    D.
    Input Value | 10 | 4 | 9 | 16
    Output value| 0|2/-2|3/-3|4/-4

    Any solutions?? I don't understand this stuff, especially at 0247hrs!
     
  4. May 6, 2004 #3

    matt grime

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    a function cannot take one input and give two outputs, it's in the definition of function.
     
  5. May 6, 2004 #4

    HallsofIvy

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    To answer the first question- Do the arithmetic!

    Saying "y=3x-2" MEANS that if x is a certain number, then y is "3 times that number minus 2". You can make up a chart of "input value and output value", like you showed,
    by choosing simple number for x (the "input value") and then calculating y (the "output value") according to that formula. The point about "identify at least 2 points" is that the graph of this is a straight line so, strictly speaking, it is determined by 2 points.

    As to 2, As Matt Grime told you- a function cannot have two different "outputs" for the same "input". (They are trying to "fool" you a little in one of those by writing fractions that can be reduced. See what happens if you reduce them.)
     
  6. May 6, 2004 #5

    matt grime

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    I read the / as an 'and' not a fraction, but the same thing applies.
     
  7. May 6, 2004 #6
    So for this x, y chart thing, it'd go something like...

    | x | y |
    | 0 | -2|
    | 2 | 4 |
    | 4 | 7 |
    | 5 | 13|

    And then the second question is kinda like reversing it?? And the / was like and/or type thing. Sorry about that. So either one of those ones could be the one with a relation but not a function??

    Thanks.​
     
  8. May 6, 2004 #7

    matt grime

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    if the input is a and the output is b AND c, then it can't be a function by definition (where b and c are different).
     
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