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Conference rusure::math

Title:Mathematics at DEC
Moderator:RUSURE::EDP
Created:Mon Feb 03 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2083
Total number of notes:14613

1608.0. "The proof of the irrational number" by HGRD01::JOSEPHCHEUNG () Mon May 11 1992 02:26

    Hello all,
                                           -2
    	As many people know how the prove 2   is irrational.
                                                -n 
    But, is it exist a general method to prove m   is irrational/
                              -4    -7
    rational ? (for example, 3   , 4  , ...)
    
    Thanks and Rgds,
    -- Joseph
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1608.1An amendment ?HGOVC::EDDIELEUNGEddie Leung @HGOMon May 11 1992 03:3711
                             (1/2)     -(1/2)
    You must be thinking of 2      or 2       and in general
              (1/n)
             m        m,n being positive integers.
    
    
    Eddie.
    
    PS :  A mathematician is someone who writes A, pronounces B but thinks
          C while actually the right answer is D.
    
1608.2SSAG::LARYLaughter & hope & a sock in the eyeMon May 11 1992 04:4316
Its a fairly simple extension of a proof known to the ancient Greeks to
prove that if n and m are integers then n^(1/m) is either an integer or
irrational; i.e. you can't have

		 1/m
		n    = p/q, q>1, p and q relatively prime

If you could, then you could raise both sides of that equation to the m-th
power to get

	n = p^m / q^m     or 	n * q^m = p^m

Since p and q have no common factors, p^m must divide n; i.e. n = k*p^m, but
then   k * p^m * q^m = p^m, or k * q^m = 1, which means that k = q = 1 and
that contradicts the premise q>1.