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Thread: Why Are these Relative Primes?

  1. #1

    Thread Starter
    pathfinder NotLKH's Avatar
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    Why Are these Relative Primes?

    I just made the following statement in something I was documenting:

    (3*c_Rows2+1)/4 and c_Rows are relatively prime

    Now, c_Rows is always odd, > 1, so 3*c_Rows2+1 is always divisible by 4.

    So my question, am I right that they are relatively prime?
    Can anyone prove it?



  2. #2
    Fanatic Member sql_lall's Avatar
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    Talking hmmm

    Let X = c_Rows (make it cleaner)

    using the fact that gcd(a,b) <= gcd(Ya, b), and <= gcd(a^2, b)

    gcd((3*X^2+1)/4, X) <= gcd(3X^2+1, X) <= gcd(3X^2+1, 3X^2)

    of course, gcd(p, p+1) = 1
    so, gcd(3X^2+1, 3X^2) = 1
    so, gcd((3*X^2+1)/4, X) <= 1

    of course, it can't be smaller, so it must = 1 !!
    sql_lall

  3. #3

  4. #4

    Thread Starter
    pathfinder NotLKH's Avatar
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    Hmmm,
    I just typed the following:

    With this Identity, it is easy to see that c_C and c_Rows are relative primes, that is, they share ABSOLUTELY NO COMMON DIVISOR WHATSOEVER, except for 1.
    Let me Quote sql_lall when she helpfully pointed out the following:
    [:clearsthroat:] Sorry for not knowing, but am I correct in referencing you as a she?


  5. #5
    Fanatic Member sql_lall's Avatar
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    hehe

    hehe...

    yeah, u are actually incorrect, i'm a he.
    Its ok though...
    i'm guessing u were taking it from my pic, or my lack of aggression or anger on other posts...the former understandable, the latter is a compliment

    Thanks for the reference anyway...i feel proud
    sql_lall

  6. #6
    Fanatic Member bugzpodder's Avatar
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    (3*x^2+1)/4 and x

    suppose some prime p divides both numbers, then p|x (p divides x) and p|3x^2+1

    but since p|x, then p|3x^2, hence p|1, so p=1
    Massey RuleZ! ^-^__Cheers!__^-^ Massey RuleZ!


    Did you know that...
    The probability that a random rational number has an even denominator is 1/3 (Salamin and Gosper 1972)? This result is independently verified by me (2002)!

  7. #7

  8. #8

    Thread Starter
    pathfinder NotLKH's Avatar
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    Hmmm,

    BTW, I corrected the she to a he, sql_lall, and you are still included in my little document.

    Which I just finished.

    Partially titled: "Why One"


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