The theorem does not apply.
1. Set the function f(x)=sqrt(x-1) equal to 0 to find what values of x make f(x) defined. So:
x - 1 is < or = to 0
x > or = to 0
2.) find the values where x is defined:
x - 1 > or = to 0
x > or = to 0
Domain = all values of x that define f(x)
[1,infinity)
{x|x> or = to 1}
DNE because 1 is not in the domain because (1-1)^1/2 = 0.