How do you graph #x^2+y^2=9# and what are its lines of symmetry?
This is the standard form for the graph of a circle!
Doesn't a circle have infinitely many lines of symmetry?
Let's look at the graph... its center will be at (0,0), and the radius = 3.
Imagine any line drawn through the center will "split" the circle in half, and can be called a line of symmetry.