Domain and range of relation

[abbycat]

I actually have 2 problems that I am struggling with. I am reviewing for a test so I am going back and attempting a few problems that I had a hard time with. I have the answers to number 3, but cannot remember how I got this? Could someone please take me through the process so that I can understand it for future reference?And for number 4, I am very confused by the wording and am completely unsure of where to begin.

 

[pka]

With respect to the first problem, is \(\displaystyle \sqrt{a}\) a real number if a < 0?

That is a typo.
\(\displaystyle \sqrt{a}\) is a real number if and only \(\displaystyle a\ge 0~.\)
Thus \(\displaystyle x+2\ge 0\).

For the range, what happens to y for all values in the domain.