powerpoint presentation for introduction of the circle
1. MG3.1 Identify and construct basic
elements of geometric figures (e.g.,
altitudes, midpoints, diagonals, angle
bisectors, and perpendicular bisectors;
central angles, radii, diameters, and
chords of circles) by using a compass
and straightedge.
2. We will identify parts of a circle and find
central angle measures
3. Warm Up
Remember when we find the percent of a
whole number we must change the
percent to a decimal and multiply.
Teacher Model
1. What is 60% of 120?
Students:
2. What is 25% of 360? WB
6. Did you know that “circle” comes from
the Greek word “Kirkos” which means
ring?
The invention of a wheel in circular
shape is considered as one of the most
important discoveries in human history.
In addition, circle is also used as a
symbol of infinity which means it is
never ending.
From Grade 7, you have learned some
terms which are related to circles such
as center, radius, diameter, chord, etc.
In this self-learning module, let us take
a deeper understanding of these
terminologies.
7. A circle is the set of all points in a plane that
are the same distance from a given point,
called the center of a circle. This distance
is called the radius of the circle.
A circle is named by its center. For
example, if point A is the center of a
circle, then the name of the circle is circle
A. There are special names for the
different parts of a circle.
How do we name a circle? Ps/nv x2
8. B
A
What is the name of this circle?
How do you know?
WB
Ps/nv x2
9. Arc
Part of a circle named
by its endpoints
Radius
Line segment
whose endpoints
are the center
of a circle and any
point on the circle
Diameter
Line segment that
passes
through the center
of a circle, and
whose endpoints lie
on the circle
Chord
Line segment whose
endpoints are any two
points on a circle
10. What color is the…
Radius?
Diameter?
Arc?
Chord?
How did you know? Ps/nv x2
wb
11. Central and Inscribed Angle
Central angle of a circle is an angle
formed by two rays whose vertex is on
the center of the circle. Each ray
intersects the circle at a point, dividing
it into arcs.
12. In the given figure at
the right, FGH is a
central angle. Its
sides divide G into
⦿
arcs. One arc is the
curve containing
points H and F. The
other arc is the curve
containing points F, E,
and H.
13. Inscribed angle
on the other hand, is an
angle whose vertex lies
along the circumference
of the circle and whose
sides contain 2 chords of
the circle. In the figure,
GMA is an inscribed
angle where vertex M
lies along the
circumference and with
sides MG and MA as
chords of the circle.
14. )
Central angle
Sector
A central angle of a circle
is an angle formed by two
radii. A sector of a circle
is the part of the circle
enclosed by two radii and an
arc connecting them.
The sum of the measures of all
of the central angles in a circle
is 360°. We say that there are
360° in a circle.
What is the sum of all central angles in a circle?
PS/WB
15. Arc
An ARC is a part of a circle that can be
classified in three different types, namely:
minor arc, major arc and semicircle
Minor Arc is an arc whose measure is
less than half of a circle. It is named by
using the two endpoints of the arc.
Major Arc is an arc whose measure is
more than half of a circle. It is named
by using the two endpoints and another
point on the arc.
16. Semicircle is an arc whose measure is
exactly one-half of the circumference of
the circle or it is an arc with a degree
measure of exactly 180 degrees. It is
named by using the two endpoints of a
diameter and another point on the arc.
It is noteworthy to mention that
in naming an arc, you can choose
the points either in clockwise or
counterclockwise manner.
18. Name the parts
of circle M.
1. Identify what you are looking for.
2. Name your starting point.
3. Name your ending point.
O
N
P
Q
R
M
A. radii:
B. diameters:
C. chords:
MN, MR, MQ, MO
NR, QO
NR, QO, QN, NP
Radii is the plural form of radius.
Reading Math
How did I/we name the radii? ps
How did I/we name the diameter?
How did I/we know ___ was a chord?
19. Name the parts of circle M.
A. radii:
B. diameters:
C. chords:
GB, GA, GF, GD
BF, AD
A
B
C
D
E
F
G
H
AH, AB, CE,
BF, AD
20. Closure
Name the parts of circle B.
1. radii
2. diameter(s)
3. chord(s)
4. What is the measure of the central angle of a
circle when the sector represents 25% of the
circle?
What is something you learned today about
circles?
BA, BC
AC
DE, FE, AC
