LESSON A:
DEFINING CIRCLES
& THEIR PARTS
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Geometry/McConaughy
1
In this lesson, you will
define circles and their
parts.
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VOCABULARY
Circle- in a plane, the set of all points
that are a given distance (radius) from
a common point (center)
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VOCABULARY
Circles are named by
their centers.
Example :
O
O
O
radius - a segment from the center of
a3/23/2016
circle to a pointGeometry/McConaughy
on the circle
________________________________
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VOCABULARY
Congruent circles- two
circles which have radii
of the same length
3 in.
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Concentric circlestwo or more circles
which share the same
center
3 in.
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NOTE: Radii, chords, and diameters
are all segments in a circle.
VOCABULARY
CHORD segment in a circle
_______________
with endpoints on the
_______________
circle
______
DIAMETER __________________
chord which intersects
__________________
a circle’s center
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NOTE: Tangents and secants are
lines of a circle .
VOCABULARY
TANGENT __________________
line which intersects a
__________________
circle in exactly one
point
__________________
Point of Tangency
SECANT __________________
line which intersects a
__________________
circle in exactly two
points
__________________
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NOTE: Central angles and inscribed
angles are angles of a circle.
VOCABULARY
CENTRAL ANGLE __________________
angle with its vertex
__________________
at the center and its
__________________
legs (sides) two radii
__________________
of
the circle
INSCRIBED ANGLE
an angle with all
__________________
points on the circle
__________________
and legs (sides)
__________________
two chords of the
__________________
circle
__________________
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Geometry/McConaughy
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An arc of a circle is two points on a
circle and the continuous (unbroken) part
of the circle between the two points.
Arc
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NOTE: Semicircles, major arcs, and
minorClassifying
arcs are arcs ofArcs:
a circle.
SEMICIRCLE Name two semicircles.
__________________
an arc of a circle
__________________
whose endpoints
Name five minor arcs.
__________________
are the endpoints
Name two major arcs.
__________________
of a diameter
MINOR ARC __________________
arc smaller than a
__________________
semicircle
MAJOR ARC arc larger than a
__________________
semicircle
__________________
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Geometry/McConaughy
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FINAL
Always use
correct CHECKS
symbols for FOR
segments,
lines, angles,
and arcs when naming circle parts.
UNDERSTANDING:
Name the following circles parts, then distinguish
among/between those in each category:
SEGMENTS LINES IN
IN CIRCLES CIRCLES
ANGLES IN
CIRCLES
ARCS IN
CIRCLES
radius
tangent
diameter
semicircle
secant
central
angle
chord
inscribed
angle
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Geometry/McConaughy
minor arc
major arc
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Homework:
Circle Parts WS
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