Doubt in (I'm Overwhelmed) Coordinate Geometry Progress Quiz #6

Hello everyone!

I’m having confusion in Q6 of (I’m Overwhelmed) Coordinate Geometry Progress Quiz #6 Solutions. At the end of the explanation, the reasoning provided for the parabola plotted across the x-axis is quite confusing for me.

It is said in the video that a parabola is cut in two halves by x axis, and that this is not even a function, because 1 x value has 2 different y values…

(https://www.gregmat.com/content/im-overwhelmed-coordinate-geometry-progress-quiz-6-solutions )

My confusion is…

When we plot a parabola that is cut in halves by Y axis does this same logic applies?

I feel I lack solid functions foundation.

No