How do you graph this equation

This question has to do with a previous ucla midterm.

The equation is:
(square root (4 - x^2)) + 3

I plugged it into wolfram alpha and got this:
http://www.wolframalpha.com/input/?i=%28…

I understand that the equation can be manipulated into:
(y-3)^2 + x^2 = 4

How do we know that this equation gives a semicircle?
Please help!

for circle standard equation form
x^2 + y^2 = r^2
y^2 =r^2-x^2
y =±√(r^2-x^2)
and + only => half circle.
+ 3 is up 3 units
center:(0,3)