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Circle Vocabulary
A Journey into the World of Circles…
Homework:Lesson 1.7/1-11, 13, 15, 19-20 all;
23 -37 odds
Definitions
Objective: Have students understand the common
definitions associated with circles such as radius, chord, and
tangent, as well as the definition of a circle itself
What is a Circle?
A circle is defined as…The set of all points in a
plane that are equidistant (radius) from a given point (center).
Circle Names
A circle is named by its center Since the center is a point we use the
circle notation and the point’s name
A
Basic Parts of a Circle
Interior of a Circle
points A, B, C
ON the circle
point D
Exterior of a Circle
points E, F, G
C
D
G
F
E
A B
Your Turn
Lesson 1.7 – CirclesTurn to pages 69 - 71Read the lessonWrite each bold faced word and its definitionOn page 70: complete the investigation on the
3 indicated circle terms
Segments of a Circle
Chord is a segment whose endpoints are on the circle
C
I
H
J
K
HI and JK arechords of C
Segments of a CircleDiameter is a chord that passes through the
center of the circle.
C
D
E
N
MED and MN arediameters of C
The Diameter is the longest chord across a circle.
Segments of a CircleRadius – a segment that has the center as one
endpoint and a point on the circle as the other endpoint.
Don’t forget… A diameter is made up of two radiiAll radii, in the same circle, are congruent
C
PPC is a radiusof C
B
A
E
CD
F
Recap…Identify the following by their correct vocabulary
name
AB - radiusAC - diameter
CD - chord
CD - secant
EF - tangentF - point of tangency
ABACCD
CD
EFF
Concentric Circles
Concentric circles are circles with a common center
and different length radii.
The region between two concentric circles of different radii is called an annulus.
ARCAn arc of a circle is the continuous part of the circle btwn the 2 endpoints.
An arc is a piece of the circle.
SemicirclesArc of a circle whose endpoints are the endpoints of a diameter of the circle. (3 letter names)
D
F
CENTRAL ANGLE-
is an angle with it’s vertex at
the center and whose legs are
radii of the circle.
A
P D
<APD is a central angle in circle P
Central Angle & Intercepted Arc
The degree measure of a central angle is equal to the degree measure of its intercepted arc.
W
X
A
INSCRIBED ANGLE
An angle with it’s vertex ON the circle and whose legs
are chords of the circle.
<AOB is an inscribed angle in circle P
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