1) Right! But if you want to be more general like in 2) you can say:

2) Right!

3) Right!

4)

Domain: First of all we now that is defined if that means in this case and in the 1th and 4th quadrant, so there are solutions between . So check again, because if domain that would mean for example would be defined, which is not.

EDIT: I see answer 3 is correct, sorry I red it wrong.