# Geometry: Circles

### Circles and Polygons

#### Inscription and Circumscription

Certain geometric figures are created by combining circles with other geometric figures, such as polygons. There are two simple ways to unite a circle with a polygon. One is inscription, and the other is circumscription.

When a polygon is inscribed in a circle, it means that each of the vertices of that polygon intersects the circle. When a polygon is circumscribed about a circle, it means that each of the sides of the polygon is tangent to the circle. Below these situations are pictured.

Figure %: A circle being inscribed and circumscribed by a polygon
Above on the left, the hexagon ABCDEF is inscribed in the circle G. On the right, the quadrilateral ABCD is circumscribed about the circle E.

#### Concentric Circles

One more brief topic to introduce is concentric circles. Concentric circles are circles that have the same center. Just because a circle is inside another circle doesn't mean they are concentric; they must have the same point as their center. Any number of circles can be concentric to one another, provided that they all share a center. Below a few are pictured.

Figure %: Concentric circles

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