I'm not sure on the following parts, I insert what I'm not sure on in () brackets.

(a) Let and be ratonal numbers satisfying . To which of the following three sets does the number belong:

(It seems fairly obvious that it's in set B but I'm not sure exactly why...)

(b) Let be a set and let be a total order on . We say that is dense if for any two with there exists such that

Consider the set

Is A dense?

(it looks as though it is dense because for every two elements you can incerease n so that you find an element between them but I wasn't 100% sure on this.)

(c) Prove that is the only positive rational number such that is an integer.

(I'm not sure what to do here, I tried to suppose that is an integer and that and then is an integer but that this only happens when , is any of that right?)

(d) How many positive real numbers x are there such that is an integer? Answer should be one of: 0,1,2,3,..., countable infinite, uncountably infinite.

(x=1 is the only rational from the previous part so its certainly not 0. But are there irrationals x such that is an integer? I don't know...)

Thanks for any help!