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Math Help - Solving Systems #2

  1. #1
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    Solving Systems #2



    I ended up with:

    a = -3c + \frac{2}{7}d + \frac{46}{7}
    b = \frac{8}{7}d + \frac{2}{7}d
    d = \frac{13}{11}

    I chose option A and option D as being true... but got it wrong. Could someone possibly take a look please?
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  2. #2
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    Quote Originally Posted by Thomas View Post


    I ended up with:

    a = -3c + \frac{2}{7}d + \frac{46}{7}
    b = \frac{8}{7}d + \frac{2}{7}d
    d = \frac{13}{11}

    I chose option A and option D as being true... but got it wrong. Could someone possibly take a look please?
    Edit (Times 2):
    You know, I'm looking at this again and I'm noting that we may use equations 1 and 3 to come up with a new equation in just b and d, which we may use together with the second equation to get values for b and d unambiguously. Then note that if we are to be able to get a consistent solution equations 1 and 3 must be the same (as a and c both have the same coefficients.) So we can only find one of them.

    Thus there is one free parameter, either a or c.

    -Dan

    PS Sorry about all the edits!
    Last edited by topsquark; September 15th 2007 at 02:08 PM. Reason: Goofed. (Again.)
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  3. #3
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    Okay, so what would the answer be? I also tried just A and that is incorrect also.
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Thomas View Post
    Okay, so what would the answer be? I also tried just A and that is incorrect also.
    I've been doing a number of "running" edits on your two problems. I think I've finally gotten it right on both of them now, but given all my previous errors, please check my logic to make sure it is sound!

    -Dan
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  5. #5
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    I tried using just Option B as an answer, and it say it's incorrect. Are any determined uniquely?

    If none are determined uniquely, I don't see how both Option A and B are wrong...
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  6. #6
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    Bump!
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  7. #7
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    Zeez, I don't get what "parameter" means here.
    When a +3c = 8 is the last standing equation, does that have one parameter or two parameters?

    Combine Eq.(1) and Eq.(3) by subtracting (3) from (1), and you get
    b -2d = -4 -------------(4)

    Play with (2) and (4), and you'd get
    b = 6
    d = 5

    Plug those into (1), and you'd get (1*) = (3)
    3a +9c = 24
    Reduce that to its simplest/lowest form,
    a +3c = 8 --------***
    Umm, I think that should be of two parameters.

    Therefore, options A,D,E should be the answer.
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  8. #8
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    The answer is B,D,E.

    You were right, minus your confusion of the parameters.

    Thank you! I am glad to finally have that question out of the way. Now only two more!
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