Sunday, January 31, 2016

abstract algebra - Irrationality of $sqrt[n]2$




I know how to prove the result for $n=2$ by contradiction, but does anyone know a proof for general integers $n$ ?



Thank you for your answers.



Marcus


Answer



Suppose that $\sqrt[n]2$ is rational. Then, for some $p,q\in\mathbb Q$,




$$\sqrt[n]2=\frac{p}{q}\implies 2=\frac{p^n}{q^n}\implies p^n=2q^n=q^n+q^n.$$



Contradiction with Fermat last theorem.


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