Which equation for parabola coordinates

[Husker70]

What equation do you use to find any cordinate on a symetrical parabola?
I've been hunting and hunting..
I have the x value.

Thanks,
Kevin

 

[Topher925]

Parabolic shapes are second order. That is

y = A*x^2 + b

If you only have x, then I would just assume A = 1 and b = 0.