18.6.2 A Regular Polygon's Center and Apothem
Core ideaA regular polygon has its own circumscribed and inscribed circles too — center to corner is the radius, center to side is the apothem, and from these you can work out both perimeter and area.
Module goal. Move from the circumference being pi times the diameter to arc length, sector area, and regular polygons, gathering geometry into quantities you can compute, and paving the way for the next stage's use of numbers and intervals to describe shapes.