Undefined Terms in Geometry

1. Undefined Terms
in Geometry
Jay Vaughn G. Pelonio, M.A.
Teacher 1

2. Short Quiz
Part 1 – Use sound deductive logic to prove these facts:
a. Ice is solid.
1. ______________________________________
2. ______________________________________
3. Therefore, Ice is solid.

3. Short Quiz
Part 1 – Use sound deductive logic to prove these facts:
b. Saturday is not a weekday.
1. ______________________________________
2. ______________________________________
3. Therefore, Saturday is not a weekday.

4. Short Quiz
Part 1 – Use sound deductive logic to prove these facts:
c. Charcoal is organic.
1. ______________________________________
2. ______________________________________
3. Therefore, Charcoal is organic.

5. Short Quiz
Part 1 – Use sound deductive logic to prove these facts:
d. Diamond is very precious
1. ______________________________________
2. ______________________________________
3. Therefore, Diamond is very precious.

6. Short Quiz
Part 1 – Use sound deductive logic to prove these facts:
e. Stress is bad for your health
1. ______________________________________
2. ______________________________________
3. Therefore, Stress is bad for your health.

7. Short Quiz
Part 2 – Use inductive logic to state these possibilities:
b. The situation could go back to normal this December.
1. ________________________________________
2. ________________________________________
3. Therefore, the situation could return to normal this December.

8. Short Quiz
Part 2 – Use inductive logic to state these possibilities:
c. There could be no classes today.
1. ________________________________________
2. ________________________________________
3. Therefore, there could be no classes today.

9. Short Quiz
Part 2 – Use inductive logic to state these possibilities:
d. I might get scolded when I get home.
1. ________________________________________
2. ________________________________________
3. Therefore, I might get scolded when I get home.

10. Short Quiz
Part 2 – Use inductive logic to state these possibilities:
d. I might get scolded when I get home.
1. ________________________________________
2. ________________________________________
3. Therefore, I might get scolded when I get home.

11. Short Quiz
Part 2 – Use inductive logic to state these possibilities:
d. I might get scolded when I get home.
1. ________________________________________
2. ________________________________________
3. Therefore, I might get scolded when I get home.

12. Undefined Terms in Geometry
There are three (3) undefined terms in Geometry:
Point Line Plane
These are undefined because it is already presumed that you know
these already. Also, it is deemed that these terms cannot be defined,
but can only be described.

13. Point
• A point is an exact position or location on a plane.
• A point has no dimensions.
• Points are named using capital letters.
A

14. Line
• A collection of points along a straight path that extends infinitely on
both sides:
• Lines are named using
• Two points: Line AB
• A small letter: Line l
A B
l
C
Points A and B are considered “collinear”
Because they are on the same line.

15. Types of Lines
• Parallel Lines – Lines on the same plane with the same slope and thus
will never meet.

16. Intersecting Lines
• Lines that intersect at a point, called the intersection.

17. Perpendicular Lines
• Are lines that intersect at a right angle

18. Plane
• A flat surface with no thickness that extends in all directions infinitely
• Planes are named using a capital letter – Plane Z
• Points A, B, and C are non-collinear but are considered “coplanar”
since they lie on the same plane, Plane Z.
.A
.B
. C Z

19. Plane
• When two (2) planes meet, a line is formed:

20. Plane
• Moreover, a plane and a line intersect at a point:

21. Activity
1. Describe the relationship of lines a and c.
2. Lines a and b intersect at point …?

22. Activity
3. Planes P and Q intersect forming line …?
4. Line B intersects planes P and Q at which points?
5. Lines b and c do not intersect. Can we consider these lines parallel?

23. Summary
• There are 3 undefined terms in Geometry: Point, Line, and Plane
• A point is an exact position or location in a plane that has no
dimensions
• A line is a set of points on a straight path that extends infinitely in
both directions
• A plane is a flat surface with no thickness that extends infinitely in all
directions

24. Online Quiz
Check the google classroom link. Make sure to finish the assessment
before the deadline.