LESSON A: DEFINING CIRCLES

& THEIR PARTS04/18/23 Geometry/McConaughy 1

In this lesson, you will define circles and their

parts.

04/18/23 Geometry/McConaughy 2

VOCABULARYCircle- in a plane, the set of all points that are a given distance (radius) from a common point (center)

04/18/23 Geometry/McConaughy 3

a segment from the center of a circle to a point on the circle

VOCABULARY

Circles are named by their centers.

O

RADIUS

radius -______________________________________________________________________

O: OExample

04/18/23 Geometry/McConaughy 4

Concentric circles- two or more circles which share the same center

VOCABULARY

Congruent circles- two circles which have radii of the same length

3 in. 3 in.

04/18/23 Geometry/McConaughy 5

VOCABULARY CHORD -

____________________________________

DIAMETER -____________________________________

NOTE: Radii, chords, and diametersare all segments in a circle.

segment in a circle with endpoints on the circle

chord which intersects a circle’s center

04/18/23 Geometry/McConaughy 6

VOCABULARY

TANGENT

SECANT

TANGENT -____________________________________

__________________

line which intersects a circle in exactly one point

Point of Tangency

SECANT -____________________________________

__________________

line which intersects a circle in exactly two points

NOTE: Tangents and secants are lines of a circle .

04/18/23 Geometry/McConaughy 7

VOCABULARY CENTRAL ANGLE -

____________________________________

__________________ __________________

INSCRIBED ANGLE -____________________________________

__________________ __________________

__________________

an angle with all points on the circle and legs (sides) two chords of the circle

angle with its vertex at the center and its legs (sides) two radii of the circle

NOTE: Central angles and inscribedangles are angles of a circle.

04/18/23 Geometry/McConaughy 8

An arc of a circle is two points on a circle and the continuous (unbroken)

part of the circle between the two points.

Arc04/18/23 Geometry/McConaughy 9

Classifying Arcs: SEMICIRCLE -

____________________________________

__________________ __________________

MINOR ARC -____________________________________

MAJOR ARC -____________________________________

an arc of a circle whose endpoints are the endpoints of a diameter

arc smaller than a semicircle

arc larger than a semicircle

NOTE: Semicircles, major arcs, andminor arcs are arcs of a circle.

Name five minor arcs.

Name two semicircles.

Name two major arcs.

04/18/23 Geometry/McConaughy 10

SEGMENTSIN CIRCLES

LINES INCIRCLES

ANGLES INCIRCLES

ARCS IN CIRCLES

FINAL CHECKS FOR UNDERSTANDING:

Name the following circles parts, then distinguish among/between those in each category:

radius

diameter

chord

tangent

secant

central angle

inscribed

angle

semicircleminor arc

major arc

Always use correct symbols for segments,lines, angles, and arcs when naming circle parts.

04/18/23 Geometry/McConaughy 11

Homework:

Circle Parts WS

04/18/23 Geometry/McConaughy 12