Sphere with Four Holes: Parametric Surface and Inscribed Circles

This example demonstrates a 3D sphere with four circular holes removed, created using parametric surface equations to form a multi-hole structure. The core mathematical concepts involve parametric surfaces, spherical coordinates, inscribed circles, and quadratic functions. Construction highlights: using GeoGebra's Surface command combined with Zip and Product functions to generate the parametric surface, with a button (button1) to toggle visibility, and lists (LA, LB, Lcos, Lind) along with index variables (ind, inX, inY, inZ) to compute hole positions and radii, with dmax and r determining hole sizes. Suitable for high school or university students learning solid geometry, parametric equations, and 3D modeling, as well as for mathematical visualization or exploring topological properties of surfaces.