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Why is pi irrational?

  1. Jun 21, 2012 #1
    Here's a question. Pi is said to be the ratio of a circle's circumference to its diameter. If this is the case, what does it say about the circumference of a circle that pi is still irrational.

    I get that pi is also used in the calculation of a circumference in the first place. Since this is true, it has to be the case that pi has been proven to be irrational independently of its definition.

    So, the question is, how did we prove pi is irrational?
  2. jcsd
  3. Jun 21, 2012 #2
    Nothing I can tell you that a quick Google search won't tell you. But one thing you might want to be aware of is that pi is also transcendental, meaning that it is the solution to no polynomial equation, or more precisely, "that is not algebraic—that is, it is not a root of a non-constant polynomial equation with rational coefficients." See: http://en.wikipedia.org/wiki/Transcendental_number

    This, in contrast, for instance, to the Golden ratio, which is irrational, but not transcendental.

    Incidentally, here is a link to another thread on this forum where the same issue was discussed at some length:

    Looking for "Easy" proof of Pi Irrational

    As for the below question...
    It's kind of mind-bending, but if you were to snip a perfect circle and stretch it out in to a straight line along an x-axis demarcated into measurement increments as small as you please, then, while that line it would be "this long" and no longer, or "this short" and no shorter, well, good luck being able to locate, or rather, specify, where exactly the endpoint of that line is relative to your 0 point.
    Last edited: Jun 21, 2012
  4. Jun 21, 2012 #3
    Halls of Ivy mentioned the following theorem in the above linked thread...

    Does anyone know where I might find a proof? That seems like a wonderful theorem.
  5. Jun 21, 2012 #4
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