What if the axis is the Y-axis? That happens when the vertex sits right on (0, y). Then the axis is x = 0, which is the Y-axis. See? The Y-axis can be the axis of symmetry, but only by coincidence.
Similarly, the X-axis can be an axis of symmetry for a sideways parabola (y = 0). But that’s rare and weird. We don’t talk about it at dinner parties.
So, final verdict: The axis of symmetry is never simply “X” or “Y.” It’s a vertical line that uses X to describe itself. Don’t confuse the label with the line itself. You’ve got this. Now go fold some parabolas like a pro.
