x^(2)+y^(2)=9

I can't get pass y=sqrt(-x^2+9)

The system I am submitting answers to says that there is a positive and a negative square root, and that the answers must be numbers. I have to find two solutions to both x and y.

Could someone just point me in the right direction as to steps to solve this?

I have a test Teus and I am so afraid I will flunk, help

!