Circles

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Lesson 8-1
Circle Terminology
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Circle Definition
Circle
The set of points coplanar points equidistant
from a given point.
The given point is called the CENTER of the
circle.
The distance from the center to the circle is
called the RADIUS.
Center
Radius
3
Definitions
Chord
The segment whose endpoints lie on the circle.
A chord that contains the center of the circle.
Diameter
Tangent
A line in the plane of the circle that intersects
the circle in exactly one point.
Tangent
Point of Tangency
Chord
The point where the tangent line intersects the
circle.
Diameter
Secant
A line that contains a chord.
Secant
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Example In the following figure identify the
chords, radii, and diameters.
Chords
Radii
Diameter
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Definitions
Congruent Circles
Circles that have congruent radii.
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2
Concentric circles
Circles that lie in the same plane and have the
same center.
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Polygons
Inscribed Polygon

• A polygon inside the circle whose vertices lie on
  the circle.

Circumscribed Polygon
A polygon whose sides are tangent to a circle.
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ARCS
Arcs

• The part or portion on the circle from some point
  B to C is called an arc.

Example
B
Semicircle
An arc that is equal to 180.
A
C
Example
8
Minor Arc Major Arc
A minor arc is an arc that is less than 180
Minor Arc
A minor arc is named using its endpoints with an
arc above.
A
Example
Major Arc
B
A major arc is an arc that is greater than 180.
B
A major arc is named using its endpoints along
with another point on the arc (in order).
A
Example
C
9
Example ARCS

• Identify a minor arc, a major arc, and a
  semicircle, given that is a diameter.

Minor Arc
Major Arc
Semicircle