What is the y intercept considered for the equation x=0?

Question

Because x=0 is graphed as a vertical on the y axis, is the y intercept for this equation undefined?

Answer 1

Because x=0 is independent of y, then y can take any value and the y intercept cannot be defined, because all values are possible. Note that y=mx+c does not cover all possible equations, but ax+by=c could, for example, be a more generally applicable form.  Or x/a+y/b=1, (bx+ay=ab, so slope-intercept form is y=-bx/a+b when a is non-zero, and m=-b/a, c=b), similar to the equation of a circle.