Using fminbnd to find point closest to origin

So I have the parabola y = x^2 − 2x − 4

The distance to the origin is d(x) = sqrt(x^2 + (x^2 − 2x − 4)^2).

So I need to plot −2 ≤ x ≤ 4 for d(x), and use fminbnd to find the point closest to the origin, and then use fzero to find the point with a distance of 3 from the origin, but I don't know how to use either of these two commands. Could anyone possibly show me an example, or with this parabola show me how to do it? Thanks.