28.7.5 Distance and Perpendicularity Combined
Core ideaThe distance from a point to a plane is the length of that perpendicular segment, and perpendicularity is the key to finding distances and heights.
Module goal. Master the tests and properties of perpendicularity for line-to-line, line-and-plane, and plane-and-plane along with the key angles, completing the pure-geometry approach and connecting to the vector method ahead.