Formalization of one optimization problem or solution of inequalities
I have checked numerically, how the region $xyz$ looks like, and the region is interesting and pretty complicated. Each shown bitmap represents a region $x\in[-1,1]\times y\in[-1,1]$ for a specific value of $z\in[0,1]$, where blue color depicts $D\ge0$ (real roots are also for $D=0$) and white imaginary roots. Also, due to its form I do not expect you can get an analytical form of this region.
