Suppose 
Now 
Since p is an integer it has a unique canonical factorisation into its prime factors in which the power to which 2 appears is an integer m.
So, if the above equation holds true m =
. (Question: Can q have a power of 2 as its factor?)
But
and we know that no integer can lie between 1 and 2. Thus we have obtained a contradiction with our original assumption that
is a rational number