Equation for Parabolic mirrors?

[Manok101]

I've been studying trig and pre calculus, and was wondering if figuring out what your parabola will look like is as simple as knowing the diameter of your circle?

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[ronin]

If parabolic y = ax² + c

It is a parabola section.

Should be able to get it from the diameter and the depth at the centre, solution depends where you want to place the y=0 "line". Across the top of the mirror or at the mirror centre.