squaring the circle

Discussion in 'Physics & Math' started by phil scalcione, Oct 30, 2003.

  1. phil scalcione tolum Registered Senior Member

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    Do I take this to mean that there is no way of calculating the area of a rectangle to be mathematically equal to the area of a circle? can this be done?
     
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  3. John Connellan Valued Senior Member

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    I think the area of a rectangle can be exactly equal to the area of a circle.
     
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  5. lethe Registered Senior Member

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    to square the circle means to construct, using a straightedge and compass, a square with the same area as a circle.

    you can only construct, with straightedge and compass, rational numbers and their square roots (and square roots of square roots, etc). pi is a transcendental number, therefore it is not constructible, therefore you cannot square the circle.
     
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  7. Absane Rocket Surgeon Valued Senior Member

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    Umm... Isn't it possible to use a straight edge and a compass to make a line sqrt(2) units long? As far as I can visualize, yes.
     
  8. Absane Rocket Surgeon Valued Senior Member

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    Wait.. that assumes you can measure out 1 unit of radius for the circle. Nevermind.
     
  9. lethe Registered Senior Member

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    yes, like i said, square roots are constructible. pi is not constructable.
     
  10. MacM Registered Senior Member

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    phik scalcione,

    Haven't heard this one since Highschool. A bit dumb now but I will never forget the surprise that we all had when our math teacher told us there was only one way to square a circle:

    (I was raised in farm country):

    "Drive a 2 x 2 up a hogs as_".
     
  11. wesmorris Nerd Overlord - we(s):1 of N Valued Senior Member

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    LOL, oh man that was funny.
     
  12. Julixa Registered Senior Member

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    mathematically it can be figured by a rectangle with on side equal to pi and the other being 1 thus pi R squared.
     
  13. 1100f Banned Registered Senior Member

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    As I once said in another thread, English is not my mother tongue, please can you explain me the joke?
     
  14. 1100f Banned Registered Senior Member

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    But if you have a side with size 1, there is no possibility to make the other side with size pi by means of a straight edge and a compass only
     
  15. Julixa Registered Senior Member

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    I take it that no areaof any circle can be a rational number? then not all areas of rectangles can be equalled by a circular area?
     
  16. MacM Registered Senior Member

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    Julixa,

    ANS: I am not a mathematician but what you say seems to be correct. If deriving the area of a circle uses multiplication by an irrational (non ending number) then the area of a circle is not actually defined and could not be duplicated by a square since the actual number is never derived.

    Would that be correct Lethe?
     
  17. lethe Registered Senior Member

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    a circle can have a rational area. for example, a circle with radius 1/Sqrt(pi) has area 1.
     
  18. MacM Registered Senior Member

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    Lethe,

    ANS: Damn. Not being a mathematician I hate having to say I disagree with a mathematician but I feel I must.

    Your solution is based on an impossible circle. You have no way of knowing what the value of a radius of pi^.5 is. Therefore you can't conclude a known area.

    What am I missing here?

    Would it not just become A = pi * ((pi^.5)^2) or pi * pi = pi^2 (still an irrational number)
     
  19. James R Just this guy, you know? Staff Member

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    He said a radius of 1/sqrt(pi), not a radius of sqrt(pi).
     
  20. MacM Registered Senior Member

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    JAmes R.,

    ANS: Ah, you are correct. But how would that change the ultimate conclusion?

    A = pi * ((1/pi^.5)^2) = pi/pi = 1. But it is still based on an unknown circle diamater.

    That is you can state it mathematically but you cannot make a known circle and square it. No circular area it seems can ever be known. You are only speaking hypothetically by making the radius a hypothetical but unknown value.

    All you are saying is if you have a circle that actually has an area = 1 then you could square that circle. But you have no way of producing such a circle.

    See my problem?
     
  21. HallsofIvy Registered Senior Member

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    Why unknown? If you are talking about actually, physically, measuring a circle of radius exactly 1/sqrt(pi), then, yes, that's impossible. But then it is also impossible to measure a distance of exactly 1/3 or, for that matter, 1. We aren't talking about measurements, we are talking about mathematics. One can always posit a length of 1, or 1/3, or pi, or 1/sqrt(pi).
    "You have no way of knowing what the value of a radius of pi^.5 is."
    I know exactly what sqrt(pi) is! No, I can't write it out in decimal form but that's not "knowing" the number, that's just knowing a particular representation.

    Julixa's post asked whether it was impossible to have a circle with rational area. The answer to that is clearly no, one can have a circle of any area- for example, the circle of radius 1/sqrt(pi) has area 1.

    It is, of course, impossible to construct a line segment of length pi (or sqrt(pi) or, for that matter, cube root of 2). As Lethe said the only numbers that can be constructed with straightedge and compass are "rational numbers and their square roots (and square roots of square roots, etc)". Technically those are called "algebraic of order a power of two".
     
    Last edited: Jan 7, 2004
  22. James R Just this guy, you know? Staff Member

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    A lot of people actually miss the point with mathematics. Maths is all about abstraction. In the real world, there are no perfect circles, straight lines extending to infinity, or equilateral triangles. But mathematics doesn't refer directly to the real world; it refers to its own world.

    It is actually a bit of a mystery as to why it is so damn useful when it comes to solving real-world problems.
     
  23. wesmorris Nerd Overlord - we(s):1 of N Valued Senior Member

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    Isn't it because it's used to form models of the real-world?
     

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