Ok for the first one we see that for any value less than two say x=1 if we put it in the function we get

and this is obviously not a real number, so any numberless than two will cause a non-real result, therefore it is out of the domain of these numbers

For the second one the same thing applies

if lets say x=0 we have

once again not a real number, the same thing occurs with any other number less than two

For the third one everything on the reals makes the function defined except x=1

the reason being if you put one in we get

and as we both know we cannot divide by zero