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Domain and range in ovals-what's this called?

  1. Oct 20, 2008 #1
    Domain and range in ovals--what's this called?

    I was helping my friend with his math homework. He's in an intermediate algebra and is working on domains and ranges of functions. He came to me for help with this method of describing domains and ranges of functions using two ovals--one listing the domains of the function and the other the range. I remember learning this in high school, so I was able to help him.

    I'm just wondering what this method is called and what it's used for.

    Thanks!
     
  2. jcsd
  3. Oct 20, 2008 #2

    symbolipoint

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    Re: Domain and range in ovals--what's this called?

    Do you really mean "ellipses" instead of "ovals"? In their full form, they are not functions, but they can be considered to be two functions put together. You can discuss domains-and-ranges of functions. Just use the definitions of DOMAIN and RANGE. Domain is the set of numbers that the independant variable can accept. Range is the set of values which the function can be.

    If "ellipse" is what you meant, then think of cutting it in half from left to right so that you have an upper part, and a lower part. Each of these parts is a separate function. The domain is the left-most x value, the right-most x value and all values of x in between.
     
  4. Oct 20, 2008 #3
    Re: Domain and range in ovals--what's this called?

    I'm sorry, I think I may have been a bit ambiguous in my description. Either that, or I just don't understand what you're trying to say. I also don't know what you mean between the difference between oval and ellipse. :P

    By "oval", I did not mean the graph of the function. I meant that there is two ovals with numbers listed inside. I have had maths up to calculus 3 and linear algebra and have never seen this method of describing points other than in algebra 1 when first learning about what constitutes a function. I also made the mistake of calling these sets of numbers together a function. The only reason I remember learning about this was to show that if there was two values assigned to a specific domain, it's not a function. I'm actually very confused as to why this method is used at all.



    For the attached picture:
    This is an example of what I'm talking about. Questions included with these diagrams would be:
    What is the domain?
    What is the range?
    Is it a function?

    The correct answer would be that the domain is the values in the 'X' oval, the range is the values in the 'Y' oval, and it would not be a function because one of the X-values has two Y-values assigned to it.
     

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  5. Oct 20, 2008 #4
    Re: Domain and range in ovals--what's this called?

    I don't know if they have a formal name--maybe something like mapping diagram or function diagram? I wouldn't be surprised if they don't have a conventional name.
     
  6. Oct 21, 2008 #5
    Re: Domain and range in ovals--what's this called?

    Blah, it worried me that this was the case. I don't understand why they test students on this. It seems like an irrelevant portrayal for such a simple to understand concept.
     
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