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

Diameter, Chord or Radius?

C

R

S

T

Lines that Intersect a Circle

C

X

Y

Lines that Intersect a Circle

Special Cases of Tangent Lines

A

C

E

F

Common Tangent TypesCommon External Tangent

Common Internal Tangent

A

C

E

F

G

H

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.

Congruent CirclesCircles are congruent circles if they have

the same length radius.

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

Minor arcsArc of a circle whose measure is smaller than 180°. (2 letter names)

S

T

Major arcsArc of a circle whose measure is between 180 ˚ and 360˚. (3 letter names)

XT

Identify a minor,a major & a semicircle arc

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

In summary…..

minor

major