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Jump in series

  1. Oct 4, 2014 #1
    Hello All

    I have got a very basic Math query here and hope people will not get turned off with the nature of this simple query.
    My query goes like this:
    variable X makes jump by factor +4.
    at the same time, Y makes a jump by factor +2

    in coordinate terms, I would have a series like :
    (4,2) (8,4) (12, 6) (16,8) (20,10)....and so on
    I would like to know the generic formula for calculting this coordinate series...for example,if Y is (say) 2867544 , then what should be X ? ( also vice versa )

    can anyone tell me a formula for this please
    ...and hope the question was clear .

  2. jcsd
  3. Oct 4, 2014 #2


    Staff: Mentor

    The jumps are not by a "factor" of 4 or 2. Factor implies things being multiplied. Here you're just adding 4 or 2 to the previous x or y value, respectively.
    All of these points are on a straight line whose equation is y = (1/2)x.
  4. Oct 4, 2014 #3


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    And, since ##x_n=4n,~n=1,2,3...## your coordinate pairs are ##(4n,2n)##.
  5. Oct 5, 2014 #4
    Thanks all . Yes my 'factor' impliction was wrongly used indeed :(
    there was another mistake of mine with the series. the actual points on the straight line are : ( 0,2,) ,(4,4) ,(8,6)....and so on.
    and I cant use y = (1/2)x here.
    and I dont think I can use (4n,2n) either. [ e.g for the 20th 'jump' , it {as per the 4n,2n) formula } should be 80,40..but actually the coordinates are (76,40) ]
    so what can I use here ....and what if 'n' is not given at all. How do I go about . In other words if only Y coordinate has been given for e.g Y is (say) 2867544 .

    I am asking this on behalf of my 12 year old kid, who has only a 'jump' till Y coordinate =62 in his textbook. Now this can be easily done with the fingers and the homework is finished :)....but I was looking for a more generic formula here & completely out of curiosity.

  6. Oct 5, 2014 #5


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    Try ##(4(n-1),2n)##.
  7. Oct 6, 2014 #6
    allright and anyway to find the 'n' too ?
  8. Oct 6, 2014 #7


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    I don't understand what you are asking. ##n## can be ##1,2,3,4...##. Find what ##n##?
  9. Oct 7, 2014 #8
    nope nothing
    I was a bit confused myself here.
    anyway...Super. Lets close this issue here now

    and Thanks all.!
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