Question

For `x=0`, does it pass the vertical line test?

Answer 1

The line `x=0` does not pass the 'vertical line test' since the vertical line `x=0` intersects with it at more than one point (in fact at rather a lot of points). So `x=0` does not define a function.

Explanation:

The equation `x=0` defines a vertical line. It does not define a function of `x`, since there a multiple values of `y` for the value `x=0`.