18.3.4 The Angle Facing a Diameter Is a Right Angle
18.3 The Inscribed Angle Theorem — Seeing the World from On the Circle
Point 4 of 5
18.3.4 The Angle Facing a Diameter Is a Right Angle
Core idea
Look across a diameter and the angle is always 90 degrees — an inscribed angle that spans a semicircle is a right angle, and the reverse holds too.
Module goal. Introduce the inscribed angle, with its vertex on the circle, and establish its half relationship with the central angle plus a run of corollaries — this is the heart of the stage.
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