Can't you continue as in the proof about ? Namely, implies that n is even and so m and n and not coprime.
How would i prove that cuberoot 2 is not rational?
Let cuberoot 2 be written in the form m/n, where m and n are coprime.
So then
Hence and thus m is divisible by 2
So there exists integer k such that m=2k
thus =
Thus =
Where do i go next? im stuck. Does it matter that its 4k^3 instead of say 2k^3? Can i just say that n^3 is thus even?