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Functional relevance?

  1. Oct 5, 2016 #1
    1. The problem statement, all variables and given/known data
    theres a table x - 1;2;3;u;u;u;u;8
    y - 370;160;90;u;24;u;u;u u - unknown value
    i have to complete this table with this equation y=(k/x)+b you have to find k and b values
    2. Relevant equations
    y=(k/x)+b x is relevant to y x -1 is y -370 and x-2 is y-160 and so on

    3. The attempt at a solution
    I have tried doing this witha calculator adding all kinds of numbers but with no progress :(.
     
  2. jcsd
  3. Oct 5, 2016 #2

    Ray Vickson

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    Are the 4 u-values in x all the same---a single unknown number---or are they 4 unknown numbers? Are the 3 u-values in y the same or different? Are the u's for x the same or different from the u's for y? Do you want an exact fit, or do you want a "best" fit, such a least-squares fit or something similar?
     
  4. Oct 5, 2016 #3
    the ones in y are different, but i believe that the ones in x might be the same, because 1;2;3 right and the last is 8 not any other number. oh and yea i guess its exact fit if yu mean like 2 or 3 not 2,5 or 3,5
     
  5. Oct 5, 2016 #4
    I just figured out something but im not sure, if k is 420 and b is -50 then it goes correctly by the table but it gets wrong at the 24, because 420/5 -50 is 34 not 24. Can it be a mistake in the table or is there smth im mistaken in ?
     
  6. Oct 5, 2016 #5

    haruspex

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    What makes you think x is 5 there?
     
  7. Oct 5, 2016 #6
    Well its mostly because the x-8 is in the end so i thought that the missing x'es were [4;7], but now i think it might not be true because the results dont match. I dont want to believe that theres a mistake in the table tho. I also thought that why are the x'es unknown if it were from 1 to 8, so i think there is some kind of secret or something that i do not know
     
  8. Oct 5, 2016 #7

    haruspex

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    Just drop the assumption that the missing x values are in arithmetic progression. The first three entries in the table are enough to find k and b. Thereafter it is just a matter of calculting the unknown number (x or y) from the known one.

    By the way, the easiest way to find k and b is to consider the product xy. This should equal k+bx, so you can do a straight line fit.
     
  9. Oct 5, 2016 #8
    so k is 420 and b is -50, the first 3 entries agree with me on this one, but i am not fluid in mathematics in english so i cant understand what you mean, do you mean xy=k+bx, sorry, and also do you think the number 24 fits in the table or is it a mistake ?
     
    Last edited: Oct 5, 2016
  10. Oct 5, 2016 #9

    haruspex

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    Yes.
    Yes.
     
  11. Oct 5, 2016 #10
    so, by my calculations x5 = 5.68 ?
     
  12. Oct 5, 2016 #11

    haruspex

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    Yes.
     
  13. Oct 5, 2016 #12

    SammyS

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    Well that's close. ##\ \frac{210}{37}=5\frac{25}{37}\ .##
     
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