Question

How do you use the vertical line test to show `x-y^2=0` is a function?

Answer 1

You can not use the vertical line test to show that `x-y^2 = 0` is a function because it is not a function

Graph for `x-y^2=0`:
graph{x-y^2=0 [-5.54, 14.46, -5.08, 4.92]}
For all `x>0` a vertical line crosses the line of the equation in two places and therefore the equation does not represent a function.