Graph 4x^2 + y^2 = 9. what are its lines of symmetry?

4 x²  + y² = 9  / : 9
x² / (9/4) + y² / 9 = 1
This is an ellipse.  Equation is:  x²/a² + y²/b² = 1
a² = 9/4  ⇒ a = 3/2
b² = 9  ⇒ b = 3
The axis of symmetry are the x and y axis, or the lines: y = 0 and x = 0.
Graph is in the attachment.