3. Circle
Defined as a locus of points that are equidistant
from a given fixed point in the plane.
The given fixed point in the plane is called the center
A Circle is named using the center.
4. Circle (Basics)
O
=
=
=
A
C D
B
A circle is the set of all points on a plane at the (equidistant)
same distance from its point in the centre.
Radius
It’s the distance from
the center of a circle
to any point on the
circle.
E
Centre
of circle
All points on the circle are
at same distance from the
centre point.
Circumference
It’s the distance around
the circle.
Diameter
It’s the distance
across a circle
through the center.
5. 1. Radius
Is a segment that connects a point on the circle to
the center.
A circle has infinite radii
D
E
10. 3. Diameter
Is a chord that passes through the center of a circle.
The longest chord on a circle..
D
E
AB DE
Its measure is twice the radius
The diameter of a circle are equal in length.
11.
12.
13.
14. 1. Secant line
Is any line that contains the chord of a circle.
A C
O
B
D
Secant line is BD
2. Tangent line
Any line that intersects at exactly
one point on the circle.
Always perpendicular to the
radius of a circle to the point of
tangency.
m
m is a tangent line
15. 3. Point of Tangency
The point of tangency is the point at which a line
intersects a circle. C is the point of tangency
A C
O
B
D
4. Common tangents
is a line that tangent to two
circles in the same plane.
m
The number of common tangents
depend on how tow circles lie on
the plane.
16. a. Separate Circles
Let us consider circles A and B that lie in the same
plane.
There will be four common tangents which can be
drawn if the two circles are separated.
17. b. Externally Tangent Circles
Circles A and C are external tangent at point D
there will be three common tangents
24. Circular arc (or Simply arc)
Portion of the circumference of a circle
Shorter than a
semicircle
Longer than a
semicircle
Semicircle an arc
that is half of a circle
Arc named by writing its endpoints under the symbol
25.
26. Identify the type of arc based on the picture and the
notation
semicircle
Minor arc
Major arc
Major arc
29. Central Angle of a Circle
Is an angle whose vertex is the center of the
circle and whose sides are the radii of the circle
C
D
O
Is the central angle to 𝑪𝑫
𝑪𝑶𝑫
m = 60°
𝑪𝑶𝑫
30. A
E
O
B
D
arc
Three categories of an arc:
1. Minor Arc
Is an arc of a circle whose measure is less than 180°
It is named using only the two
endpoints of the arc.
Example of minor arcs:
𝑩𝑫 𝑨𝑩 𝑨𝑬 𝑬𝑫
m = m∠EOD = x◦
𝑬𝑫
31. A
E
O
B
D
arc
Three categories of an arc:
2. Major Arc
A portion of a circle whose measure is more than
the semicircle.
It is named by three points on the
circle.
𝑬𝑩𝑫 𝑬𝑨𝑫 𝑩𝑫𝑨 B𝑬𝑨
m = 360° − 𝒎 = 360° − x◦
𝑬𝑩𝑫
Measures more than 180°
Its obtained by subtracting the
measure of its corresponding
minor arc from 360°
A𝑫𝑬 A𝑩𝑬
𝑬𝑫
32. A
E
O
B
D
arc
Three categories of an arc:
3. Semicircle
An arc whose measure is exactly 180°
Its endpoints are the endpoints of
the diameter.
𝑨𝑩𝑫 𝑩𝑫𝑬 𝑫𝑬𝑨 EAB
m = 1𝟖𝟎°
𝑨𝑩𝑫
It is named using the two
endpoints and a points and a
point in between the
endpoints
33. 𝑬𝑮
𝑬𝑹𝑮
𝑬𝑮
The measure of the central angle is equal to the
measure of its intercepted arc
88°
E
G
Q
R
𝑬𝑹𝑮
𝑬𝑮
Given circle Q, find m
and m
Solution:
m∠EQG = 88° , m = 88°
m = 360° − m
= 360° − 𝟖𝟖° = 𝟐𝟕𝟐°
34. 𝑩𝑬𝑪
𝑫𝑬𝑪
𝑩𝑫
𝑫𝑪
𝑩𝑪
𝑫𝑩
ARC Addition Postulate
The measure of an arc formed by two adjacent non-
overlapping arcs is a sum of the measures of those two arcs.
A
B
C
D
E
m + m = m and
m + m = m
Example: By the Arc Addition
Postulate
35. Example:
Referring to P , provide what is asked
.
a. Name a radius.
C
D
E
A
B
P
CP DP EP AP BP
b. Name a diameter BD
c. Name of central angle
∠𝐶𝑃𝐷 , ∠𝐷𝑃𝐸 , ∠𝐴𝑃𝐸, ∠𝐵𝑃𝐴
, ∠𝐶𝑃𝐵 , ∠𝐶𝑃𝐸, ∠EPB , ∠𝐷𝑃𝐴,
∠𝐶𝑃𝐴
36. Example:
Referring to P , provide what is asked
.
d. Name a minor arc
C
D
E
A
B
P
e. Name of major arc
𝑨𝑩 𝑨𝑬 𝑬𝑫 𝑪𝑫 𝑩𝑪
𝑨𝑪 𝑪𝑬 𝑨𝑫 𝑬𝑩
𝑨𝑪𝑬 𝑪𝑩𝑬 𝑩𝑪𝑬 𝑨𝑫𝑪
𝑩𝑫𝑨 𝑩𝑪𝑨 𝑩𝑬𝑨 𝑨𝑩𝑬
𝑨𝑩𝑫
37. Example:
Referring to P , provide what is asked
.
f. Name a semicircle
C
D
E
A
B
P
g. Name the minor arc relative to ∠𝑪𝑷𝑫.
𝑩𝑪𝑫 𝑩𝑨𝑫 𝑩𝑬𝑫
𝑪𝑫
h. Name a major arc relative to
∠𝑨𝑷𝑬
𝑨𝑪𝑬 𝑨𝑩𝑬 𝑨𝑫𝑬
38. 𝑩𝑬𝑫
Example:
Referring to P , provide what is asked
.
i. What is m
C
D
E
A
B
P
𝑫𝑬
j. If the m ∠𝑫𝑷𝑬 = 𝟖𝟎, what is m
180
𝑫𝑬
m = 80
k. If the m ∠𝑩𝑷𝑨 = 𝟑𝟎,
what is m 𝑩𝑪𝑨
𝑩𝑪𝑨
m = 𝟑𝟔𝟎 − 𝟑𝟎 = 𝟑𝟑𝟎
39. Identify whether each arc is a minor arc, major arc, or a
semicircle.
D
A
F B
a. FE
C
E
G
35°
2𝟎°
1𝟑𝟓°
b. DE
c. FEB
d. FGB
e. EGD
40. Determine the measures of the following arcs:
D
A
F B
a. CB
C
E
G
35°
2𝟎°
1𝟑𝟓°
b. DC
e. EB
f. EGB
g. EBG
h. CFB
c. FG
d. CG