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Math Help - help please-hard question

  1. #1
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    help please-hard question

    The points (−1, 2) and (−1, 1) satisfy a relation R, which of the following can we (definitely) conclude?


    Select one:
    a. R is a function
    b. R is not a function
    c. R is y=-1
    d. R is x=-1
    e. None of the above

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    Re: help please-hard question

    This is not a hard question. Tell us what you have tried so far.
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    Re: help please-hard question

    Quote Originally Posted by mathkid182 View Post
    The points (−1, 2) and (−1, 1) satisfy a relation R, which of the following can we (definitely) conclude?


    Select one:
    a. R is a function
    b. R is not a function
    c. R is y=-1
    d. R is x=-1
    e. None of the above

    Do you understand that functions work by putting a number in and getting a single number out?

    What's happening in your case with the number you're putting in? (i.e. x = -1)
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    Re: help please-hard question

    not to worry sorry i figured out that because it has the same -1 on both plots it is not a function.

    what about this one-
    The points (1, 3) and (2, 3) satisfy a relation R, which of the following can we (definitely) conclude?

    Select one:
    a. R is a function
    b. R is not a function
    c. R is y=3
    d. R is a straight line
    e. None of the above

    I know its a straight line and is function but neither answers are right? what would be the right answer?
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    Senior Member Paze's Avatar
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    Re: help please-hard question

    Quote Originally Posted by mathkid182 View Post
    not to worry sorry i figured out that because it has the same -1 on both plots it is not a function.

    what about this one-
    The points (1, 3) and (2, 3) satisfy a relation R, which of the following can we (definitely) conclude?

    Select one:
    a. R is a function
    b. R is not a function
    c. R is y=3
    d. R is a straight line
    e. None of the above

    I know its a straight line and is function but neither answers are right? what would be the right answer?
    Look at the co-ordinates you are given and see if you notice a trend.

    Also, in the future, please post in the appropriate forum. You have posted in the calculus forum. This belongs to 'algebra'.
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    Re: help please-hard question

    Quote Originally Posted by Paze View Post
    Look at the co-ordinates you are given and see if you notice a trend.
    A trend is irrelevant to the possibility of making a definite conclusion.
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    Member Ruun's Avatar
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    Re: help please-hard question

    Suposse that your given ordered pairs belong to the cartesian product that defines a function. Then they will be in the form (x,f(x)). Now recall the definition of a function, in particular about the uniqueness about f(x)
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    Re: help please-hard question

    Quote Originally Posted by mathkid182 View Post
    not to worry sorry i figured out that because it has the same -1 on both plots it is not a function.

    what about this one-
    The points (1, 3) and (2, 3) satisfy a relation R, which of the following can we (definitely) conclude?

    Select one:
    a. R is a function
    b. R is not a function
    c. R is y=3
    d. R is a straight line
    e. None of the above

    I know its a straight line and is function but neither answers are right? what would be the right answer?
    No, you don't know either of those things. For example the relation containing pairs {(1, 3), (2, 3), (1, -3)} and y= x for x not equal to 1 or 2 is not a function nor a straight line but sastisfies the conditions. You seem to be under the impression that since we have both (1, 3) and (2, 3) we must have "y= 3" for all x. That is possible but not necessary.
    Thanks from BenBrawn
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    Senior Member Paze's Avatar
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    Re: help please-hard question

    Quote Originally Posted by emakarov View Post
    A trend is irrelevant to the possibility of making a definite conclusion.
    But by noticing the trend, you should be able to come up with a definite conclusion, yes?
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    Re: help please-hard question

    Quote Originally Posted by Paze View Post
    But by noticing the trend, you should be able to come up with a definite conclusion, yes?
    As HallsofIvy describes, in this case the trend is misleading. It does not follow that R has properties (a)-(d).
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    Senior Member Paze's Avatar
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    Re: help please-hard question

    Quote Originally Posted by emakarov View Post
    As HallsofIvy describes, in this case the trend is misleading. It does not follow that R has properties (a)-(d).
    I don't understand. We have the points (1,3) and (2,3) and we are to conclude a relation between these points. y=3 in both points so how come this does not satisfy a 'relationship' between these two points? Nobody said anything about all x. Or maybe I am misunderstanding?
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    Re: help please-hard question

    Quote Originally Posted by Paze View Post
    We have the points (1,3) and (2,3) and we are to conclude a relation between these points. y=3 in both points so how come this does not satisfy a 'relationship' between these two points? Nobody said anything about all x. Or maybe I am misunderstanding?
    Yes, the question is about all x. That is, the question is about R as a whole, about all pairs (x, y) in R. And it asks not what type of R could contain (1, 3) and (2, 3), but what statements about R follow with necessity. Neither of statements (a)-(d) do.
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    Re: help please-hard question

    Quote Originally Posted by mathkid182 View Post
    not to worry sorry i figured out that because it has the same -1 on both plots it is not a function.

    what about this one-
    The points (1, 3) and (2, 3) satisfy a relation R, which of the following can we (definitely) conclude?

    Select one:
    a. R is a function
    b. R is not a function
    c. R is y=3
    d. R is a straight line
    e. None of the above

    I know its a straight line and is function but neither answers are right? what would be the right answer?
    my 2cents worth:
    a) and c).
    R is not a straight line. Plot it. Does it look like a straight line? It looks like two points to me.
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