Thursday, April 6, 2017

Is this sufficient to prove $sqrt{n}$ is irrational if $n$ is not a perfect square



If $n$ is a natural number then $n$ is a unique product of primes to integer powers



If $n$ is a perfect square then its prime factors will all be to even powers hence when taking the square root the results prime factors will be to integer powers hence the square root is an integer.




If $n$ is not a perfect square then at least one prime factor is to an odd power. Hence its square root will have a prime to a non integer power but all integers can be written as a product of primes to an integer power hence $\sqrt{n}$ cannot be an integer.



Is this sufficient to prove all square roots of non perfect squares is irrational?


Answer



I think there is one assumption that you are implicitly using: The prime factorization of $n$ could have more than one prime - let us say $p$ and $q$ - with an odd exponent. In this case you'd have to prove for instance that $p^{1/2} q^{1/2} \not \in \mathbb Z$.


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