For what you have is perfectly acceptable. If you like you could distribute the negative by multiplying everything in the numerator by -1.

i.e. .

is fine. To find , just take the negative of . So do exactly what I suggested for .

What you've done with is fine too. Just do what I suggested with and . It's even, because if you do a little more work, you can get .

To find the domain of a function, it is usually easiest to get y in terms of x.

So for the first one...

Multiply everything by y

Get all the y's on one side...

Complete the square...

.

Now solve for y...

.

Now you should be able to analyse the right hand side to find the domain.

Clearly what is under the square root can't be negative, so...

.

So the domain is .

For the second one, just square both sides and you have y = something. Analyse the right hand side.