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Simultaneous Dysfunction

  1. Apr 24, 2014 #1

    Atomised

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    1. The problem statement, all variables and given/known data

    Solve:

    (A) 1.7x + 2.3y = 3.5

    (B) 2.8x + 3.2y = -9.5


    2. Relevant equations

    Without using quadratic formula.

    3. The attempt at a solution

    I hate to admit it but I am having trouble with this. Seems to lead to monstrous calculations.

    I tried subtracting B/4 from A to get x + 3.1 y = 5.875.

    Also, substituting letters for numbers.

    Is there something I'm missing or is this just a very tedious calculation?
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Apr 24, 2014 #2

    Ray Vickson

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    You have made a start; now just keep going. You have x = 5.875 - 3.1 y, so now wherever you see x you can substitute in that above expression. That will give you an equation involving y alone. That will then be easy to solve. OK: it is messy and takes time, but welcome to equation solving.
     
  4. Apr 24, 2014 #3

    Atomised

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    Thanks - I realise I made a stupid mistake which unnecessarily complicated things.
     
  5. Apr 24, 2014 #4

    SteamKing

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    Why would you think the quadratic formula would be used in solving simultaneous equations?
     
  6. Apr 24, 2014 #5

    Atomised

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    My cack-handed manipulations resulted in x's on LHS and reciprocal y's on RHS. Thanks for your all help - it is a tremendous resource.
     
  7. Apr 24, 2014 #6

    HallsofIvy

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    By the way, where did you get the word "Dysfunction"? Is that a translation from another language?
     
  8. Apr 25, 2014 #7

    Atomised

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    Just means pathological. Greek in origin.


    I have proven that the problem I am currently working on is non-understandable at x_n, for all n.
     
  9. Apr 25, 2014 #8

    Mark44

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    It's not really a complicated problem ("monstrous calculations" is really hyperbole). It's just a system of two linear equations, which is about the simplest possible system you could be given. Each of the equations represents a line, and the solution of the system is the point at which the lines intersect. A very cursory inspection of the two equations is enough to say that there is a unique solution to the system.
     
  10. Apr 25, 2014 #9

    Atomised

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    Easy in principle. I was frustrated by my apparent inability to juggle six figure decimals (even with HP42S to help, me the world's best calculator).


    I have proven that the problem I am currently working on is non-understandable at x_n, for all n.
     
  11. Apr 25, 2014 #10

    Mark44

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    You have proven that you write things that you don't understand...
     
  12. Apr 25, 2014 #11

    Mentallic

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    What does "non-understandable" mean? You may want to post the entire problem, because your proof already sounds a little misconstrued.
     
  13. Apr 25, 2014 #12

    Mark44

    Staff: Mentor

    It's not a proof - the exercise is just to find the solution of a system of two linear equations.

    The "non-understandable" bit is just the OP being dramatic, IMO.
     
  14. Apr 25, 2014 #13

    Atomised

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    The 'non-understandable' was just the supposedly witty signature comment set on my PF app. Now removed.
     
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