Quick Recap — 3D Geometry (Hard)

Chain the tools: foot/image of a point in a plane (shift along the normal by ax1+by1+cz1+da2+b2+c2\tfrac{ax_1+by_1+cz_1+d}{a^2+b^2+c^2}, doubled for the image), direction cosines, angles, and parallel-plane distances. Many are numerical-value (Section B), with cross-topic links to vectors.