Circle Vocabulary
C
Circle – set of all
points equidistant
_________
from a given point
called the _____
center
of the circle.
Symbol:
C
CHORD:
A segment
whose
endpoints
are on the
circle
DIAMETER:
P
Distance
across the
circle through
its center
Also known as the
longest chord.
RADIUS:
P
Distance
from the
center to
point on
circle
Formula
Radius = ½ diameter
or
Diameter = 2r
WRITE THIS DOWN AND TELL
ME WHY
ALL CIRCLES ARE
SIMILAR
D = ?
r = ?
r = ?
D = ?
Use P to determine whether each
statement is true or false.
Q
1. RT is a diameter. False R
2. PS is a radius. True
P
3. QT is a chord. True
T
S
Secant Line:
intersects the
circle at
exactly TWO
points
Tangent Line:
a LINE that intersects the circle
exactly ONE time
Forms a 90°angle
with one radius
Point of Tangency:
The point where the
tangent intersects
the circle
Name the term that best describes the notation.
Central Angles
An angle whose vertex is
at the center of the circle
3 Types of Arcs
A
Major Arc
Minor Arc
More than 180°
Less than 180°
P
ACB
To name:
use 3 letters
C
AB
B
To name:
use 2 letters
APB is a Central Angle
Semicircle: An Arc that equals 180°
D
E
To name:
use 3 letters
P
F
EDF
THINGS TO KNOW AND
REMEMBER ALWAYS
A circle has 360 degrees
A semicircle has 180 degrees
Vertical Angles are CONGRUENT
Linear Pairs are SUPPLEMENTARY
Formula
measure Arc = measure Central Angle
Find the measures.
EB is a diameter.
m AB = 96°
A
E
m ACB= 264°
Q
m AE = 84°
96
B
C
Arc Addition Postulate
A
C
B
m ABC = m AB + m BC
Tell me the measure of the following arcs.
AC is a diameter.
m DAB =240
m BCA = 260
D
C
140
R
40
100
80
B
A
Congruent Arcs have the same measure and
MUST come from the same circle or of
congruent circles.
C
B
A
45
45
D
110
Arc length is proportional to “r”
Textbook
p. 396 #11
p. 404 #11 – 16, 25 – 30, 38