1. LESSON A: DEFINING CIRCLES & THEIR PARTS
4/16/2017
Geometry/McConaughy

2. In this lesson, you will define circles and their parts.
4/16/2017
Geometry/McConaughy

3. VOCABULARY
Circle-
in a plane, the set of all points that are a given distance (radius) from a common point (center)
4/16/2017
Geometry/McConaughy

4. VOCABULARY RADIUS Circles are named by their centers. O O
a segment from the center of a circle to a point on the circle
radius -________________________________ ______________________________________
4/16/2017
Geometry/McConaughy

5. VOCABULARY
Concentric circles- two or more circles which share the same center
Congruent circles- two
circles which have radii
of the same length
3 in.
3 in.
4/16/2017
Geometry/McConaughy

6. VOCABULARY NOTE: Radii, chords, and diameters
are all segments in a circle.
CHORD -____________________________________
segment in a circle with endpoints on the circle
DIAMETER -____________________________________
chord which intersects a circle’s center
4/16/2017
Geometry/McConaughy

7. NOTE: Tangents and secants are
lines of a circle .
VOCABULARY
TANGENT
TANGENT -____________________________________
__________________
Point of Tangency
line which intersects a circle in exactly one point
SECANT -____________________________________
__________________
line which intersects a circle in exactly two points
SECANT
4/16/2017
Geometry/McConaughy

8. VOCABULARY 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
4/16/2017
Geometry/McConaughy

9. An arc of a circle is two points on a circle and the continuous (unbroken) part of the circle between the two points.
Arc
4/16/2017
Geometry/McConaughy

10. Classifying Arcs: NOTE: Semicircles, major arcs, and
minor arcs are arcs of a circle.
SEMICIRCLE -____________________________________
__________________
Name two semicircles.
an arc of a circle whose endpoints are the endpoints of a diameter
Name five minor arcs.
Name two major arcs.
MINOR ARC -____________________________________
arc smaller than a semicircle
MAJOR ARC -____________________________________
arc larger than a semicircle
4/16/2017
Geometry/McConaughy

11. FINAL CHECKS FOR UNDERSTANDING:
Always use correct symbols for segments,
lines, angles, and arcs when naming circle parts.
FINAL CHECKS FOR UNDERSTANDING:
Name the following circles parts, then distinguish
among/between those in each category:
SEGMENTS
IN CIRCLES
LINES IN
CIRCLES
ANGLES IN
ARCS IN CIRCLES
radius
tangent
central angle
semicircle
diameter
secant
minor arc
chord
inscribed
angle
major arc
4/16/2017
Geometry/McConaughy

12. Homework:
Circle Parts WS
4/16/2017
Geometry/McConaughy