Circumscribed and Inscribed Circles and Polygons
A circle is circumscribed about a polygon if the polygon's vertices are on the circle. For triangles, the center of this circle is the circumcenter. A circle is inscribed a polygon if the sides of the polygon are tangential to the circle. For triangles, the center of this circle is the incenter. Circumscribed and inscribed circles show up a lot in area problems.