Consider 3√17. Like the famous proof that √2 is irrational, I also wish to prove that this number is irrational. Suppose it is rational, then we can write:
17=p3q3.
and then
17q3=p3
With the proof of √2 we used the fact that we got an even number at this step in the proof and that p and q were in lowest terms. However, 17 is a prime number, somehow we could use this fact and the fact that every number has a unique prime factorisation to arrive at a contradiction, but I don't quite see it yet.
Answer
The argument that works with 2 also works with 17. Since 17q3=p3, 17∣p3 and therefore 17∣p. Can you take it from here?
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