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Need Equation/graphing help

  1. Sep 20, 2004 #1
    I know next to nothing about this stuff, and have a problem that is due Monday... I have signed up with a tutor, but not able to begin studies until Thursday....
    Anyway, my problem is as follows:

    We are to solve for x and y using addition, subtraction and subsitution, and then graphicly, min of three points....

    I would be thankful for any help......... Skyie :confused:
  2. jcsd
  3. Sep 20, 2004 #2


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    Welcome to PF!
    "x" and "y" are some two numbers, right?
    (You don't know at the moment their values)
    So, the first equation says:
    This means, that whatever values "x" and "y" have we have been told that "y" is equally big as 3 times x minus 4 (right?)
    So, whenever we meet "y" (for example in your second equation), we might substitute 3x-4 for "y" (that expression has, by our first equation, the same value as "y")
    Does this help you?
  4. Sep 20, 2004 #3
    Hello I am hoping someone can help. My daughter has an equation she does not understand and I am unable to help her.

    -5/8 x 16/21 x (-7/15)

    I cannot seem to figure out what the common denominator would be for her to be able to work her way through this

    Can anyone help????
  5. Sep 20, 2004 #4


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    Hi, sdmcam :welcome to PF!
    (Just a note: Please don't hijack another person's yhread in the future, post your own :smile:)

    Now, as far as I can tell, you've gor an expression here which you want to simplify?
    Is the "x" a multiplication sign?
  6. Sep 20, 2004 #5


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    First, this is not an equation, it is an "expression" (it's not an equation because it's not equal to anything).

    Secondly, multiplying fractions, you don't need to find a "common denominator"- that's used in adding or subtracting fractions.


    Notice that one fraction has 8 in the denominator and another has 16 in the numerator: 16/8= 2. One fraction has 5 in the numerator and the other has 15 in the denominator: 5/15= 1/3. One fraction has 21 in the denominator and another has 7 in the numerator: 7/21= 1/3. Finally, (-)(-)= +.

    This is the same as
    [tex]\frac{2}{(3)(3)}= \frac{2}{9}[/tex].
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