# Irrationality of square root of 2 [closed]

It is possible to explain me the 18th proof of the irrationality of square root of 2 from the following site? http://www.cut-the-knot.org/proofs/sq_root.shtml

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## closed as not a real question by Robin Chapman, Scott Morrison♦Jun 26 '10 at 18:22

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The proof looks perfectly clear to me, except for a typo; CG=CD should be CG=GD (which is correctly stated earlier). What needs explanation? (This doesn't seem appropriate for MathOverflow.) –  Andreas Blass Jun 26 '10 at 17:31
Closed, please check the FAQ. –  Scott Morrison Jun 26 '10 at 18:24
Christian: on a side note, you may like the analogous elementary proof of the irrationality of the other classic number, the golden ratio. Since it verifies the relation x=1+1/x and 1<x<2, if x were rational, x=p/q with 0<q<p, then also x=q/(p-q), and 0<p-q<q so there is no minimal denominator, a contradiction. –  Pietro Majer Jun 26 '10 at 18:33
-1 for not saying what the questioner doesn't understand... –  Yemon Choi Jun 26 '10 at 19:37
In the future, you'd have better luck directing such questions to sites like artofproblemsolving.com. –  Qiaochu Yuan Jun 26 '10 at 22:09