A circle that passes through all vertices (corner points) of a polygon.

Triangles, rectangles, regular polygons and some other shapes have an incircle, but not all polygons.

A regular polygon's radius is also the radius of the circumcircle.

Below is the circumcircle of a triangle (try dragging the points):

Triangles, rectangles, regular polygons and some other shapes have an incircle, but not all polygons.

A regular polygon's radius is also the radius of the circumcircle.

Below is the circumcircle of a triangle (try dragging the points):

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