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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.

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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