18.1.5 Putting the Perpendicular Diameter to Work
Core ideaKnowing the chord's length and how far the center sits from it, you join up a right triangle and use the Pythagorean theorem to find the radius r.
Module goal. Start from the one core idea — every point the same distance from a fixed center — to understand the circle, then unearth its most powerful weapon, symmetry, laying the foundation for every theorem to come.