28.7.4 Tests and Properties of Perpendicular Planes
Core ideaIf one plane contains a line perpendicular to another plane, the two planes are perpendicular; run the reasoning backward to get a line perpendicular to a plane.
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.