Friday, 26 July 2013

arithmetic - integral factors of an irrational number



If the radicand of a square root is a non-square (making the root an irrational), and if the non-square is either a prime number, or a composite number that does not have a square divisor (other than 1), does this mean that the square root is not divisible by an integral divisor (that it does not have an integral factor)?



For example, 200=100×2=100×2=102, so 200 has an integral factor of 10 (is divisible by 10). However, 6=3×2=3×2



I'm mainly wondering for the purpose of reducing fractions that contain radicals and integers.


Answer




The phrase "does not have an integral factor" is a little imprecise, since anything has an integral factor: we have x=17(x17).



So we rephrase the question. Suppose that n is a square-free integer. Do there exist integers d and k, with k>1, such that
n=kd?


Once we express the question like that, the answer is quick. Suppose to the contrary that there are integers k,d, with k>1, such that (1) holds. Squaring both sides, we get n=k2d, so n is divisible by a square greater than 1.


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