A demo lesson focusing the definition of a circle and the geometric figures related to it such as the points, segments, and lines related to it.

1. Points
Segments Lines

2. PICTURE!
PICTURE!

3. •
G
O•
D
•
Bangui
Windmills
by Agnes Manalo
from Google Images

4. L
V
E
O
S
LEO The Lion
by stylecraze
from Google Images

5. Zipline
from Google Images
Y
O

7. D
E
F
I
N
I
T
I
O
N
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.
A

8. LET’S EXPLORE!
Using circle A,
1. Draw the following
points:
a. L inside circle A;
b. G outside circle A;
c. N, I, C, and E on circle A.

9. P
O
I
N
T
S
N
G
L
A
A
I
Interior
points
Exterior
points
E
A
C
Points on
the circle

10. LET’S EXPLORE!
Using circle A,
2. Connect the
following points:
a. A and I;
b. C and N;
c. E and C.

11. S
E
G
M
E
N
T
S
radius
A
chord diameter
C
N
A
A
E
I
AI is a radius
of
A
C
NC is a chord
of
A
EC is a diameter
of
A

12. Definition:
Radius
Line segment
whose endpoints
are the center of
a circle and any
point on the circle

13. Definition:
Chord
Line segment whose endpoints
are any two points on a circle

14. Definition:
Diameter
Line segment that
passes
through the
center of a circle,
and whose
endpoints lie on
the circle

15. LET’S EXPLORE!
3. Compare the measures
of the segments AI, AE
and AC.
4. How is the measure of
segment EC related to the
measures of segments AI,
AE, and AC?

16. S
E
G
M
E
N
T
S
radius
A
chord diameter
C
N
A
A
E
I
AI is a radius
of
A
C
NC is a chord
of
A
EC is a diameter
of
A
Note:
All radii of the same circle are congruent.
The diameter is twice the radius.
The diameter is the longest chord in a circle.

17. LET’S EXPLORE!
Using circle A,
3. Draw a line
containing the points:
a. E and G;
b. I and C;

18. L
I
N
E
S
secant
tangent
C
G
A
E
EG is a tangent
of
A
I
A
IC is a secant
of
A

19. Definition:
• A line is tangent to
the circle if it
touches it just once.
Such a line is called
a tangent or a
tangent line. The
point where the
tangent touches the
circle is called the
point of tangency.
• We can also speak
of tangent
segments or rays.
Tangent

20. Definition:
Secant
• A line that intersects
the circle twice is
called a secant line or
a secant.
• Line segments and
rays may also be
secants.
• Often, secants are
drawn from a point
outside of the circle to
a point on the circle.

21. Identify each of the following as related to ʘ A.
1. A
2. RP
3. PI
4. SR
5. IS
6. PE
7. AR
8. SI
9. AS
10. P

22. Name each of the following:
1. a circle
2. one interior point
3. four exterior points
4. four points on the
circle
5. center
6. two points of
tangency
7. four radii
8. a chord
9. two diameters
10. two tangents
11. a secant

23. Work in pairs and try this!
Using the circle at the right,
A. Draw:
(1) radius HJ;
(2) diameter IC;
(3) chord IS;
(4) a line passing
through points H and R;
(5) line ST

24. Work in pairs and try this!
Using the circle at the right,
B. Connect the points:
(6) T and C;
(7) C and H
(8) H and I

25. Work in pairs and try this!
Using the circle at the right,
C. Name the following:
(9) a circle;
(10) an exterior point
(11) a tangent line
(12) a secant line
(13) a point of tangency
(14 - 16) three radii
(17 - 20) four chords (aside
from IS or SI)

26. Answers:
R
H
C
I
J
T
S
9. J
10. R
11. HR or RH
12. TS or ST
13. H
14 -16. HJ or JH
IJ or JI
CJ or JC
17 - 20
HI or IH
CT or TC
CH or HC
ST or TS

27. S
E
G
M
E
N
T
S
radius
A
chord diameter
C
N
A
A
E
I
AI is a radius
of
A
C
NC is a chord
of
A
EC is a diameter
of
A

28. L
I
N
E
S
secant
tangent
C
G
A
E
EG is a tangent
of
A
I
A
IC is a secant
of
A

29. Points
Segments
Lines

30. Points
Segments

31. Points