Answer:
The expression is unclear so:
If the denominator is
then your set of existence is given by
since you want the quantity inside both square roots to be positive (and it happens for both to be simply
and you don't want a zero at the denominator so you have to rule out 1.
If the square root includes the whole denominator
the condition becomes 
where you don't include the extreme in the second condition since, again, you don't want to divide by 0. The answer in this case is simply
since values between 0 and 1 will give a negative root which is not a real number.