First lesson for Grade 8 stem geometry

1. Shapes in Motion:
Introduction to Geometry
Jay Vaughn G. Pelonio, M.A.
Teacher 1

2. History of Geometry
Geometry has been practiced since the ancient times
• To calculate land area
• Estimate the earth’s radius
• Calculate heights of tall objects (i.e. mountains, walls, etc.)
• Calculate position using the stars
• And many, many more!

3. History of Geometry (cont.)
The Greek mathematician Euclid, often referred to as the “Father of
Geometry”, revolutionized the study of Geometry .
Euclid of Alexandria

4. Activity: Pick the Odd one Out!
Directions: Select and cross-out the shape that you think does not
belong to the group. Send your answers to my email.
Set 1:

5. Activity: Pick the Odd one Out!(cont.)
Set no.2:
Set no.3:

6. Activity: Pick the Odd one Out (Answers)
Set 1:
The third figure was crossed out because it is not symmetric, unlike the
other three (3).

7. Set 2:
The second figure was crossed out because it is symmetric, unlike the
other three (3).
Activity: Pick the Odd one Out (Answers)

8. Activity: Pick the Odd one out! (Answers)
Set no. 3:
All of the figures are symmetric, but the third figure doesn’t have
rotational symmetry so it is crossed out.

9. Reflection:
What is the difference between symmetry and
asymmetry?

10. Definition of symmetry
Symmetry refers to an object having similar or proportional
parts along a point or axis.
Meanwhile, asymmetric shapes are unbalanced, and therefore
are not proportionate along a point or axis.

11. Types of Symmetry:
a. Reflective Symmetry
When a part of an object looks similar to another part when divided
along a line or axis, then that object is said to have reflective symmetry
along the line of symmetry. Line of symmetry

12. Types of Symmetry (cont.)
b. Rotational Symmetry
When an object is rotated, and it coincides and looks similar in one way or
another to its original form then that object has rotational symmetry. The
central point of the object where it is rotated is called the center of
symmetry.
Center of symmetry

13. Order of rotational symmetry
The number of times a figure coincides with its original position during the
complete turn is called its order of rotational symmetry:

14. Review
1. Differentiate symmetry and asymmetry.
2. What are the 2 types of symmetry?

15. Importance of Symmetry and Asymmetry
Symmetry is important not only for aesthetics but also in the field of
construction, ensuring a structure’s integrity and stability:

16. Importance of Symmetry and
Asymmetry(cont.)
Assymetry is also important, not only to create visual variations but it is
also a necessary aspect especially in biological systems:
The left and right lungs are asymmetric to
give way for the Heart.

17. Summary
a. Geometry is a branch of mathematics that
studies the sizes, shapes, positions, angles,
and dimensions of things.

18. Summary
b. The Greek mathematician Euclid
revolutionized the study of Geometry with
his collection of works and studies.

19. Summary
c. Symmetrical objects project a property of
balance, while asymmetric objects do not.

20. Summary
d. Objects with reflective symmetry are
symmetric to its other half along a line of
symmetry
e. Objects with rotational symmetry have a
central point called the center of symmetry.

21. Assessment: Online Quiz
Directions: Answer the following question using MS Word. Sumbit your
files to my email.
1. How did the early civilizations use geometry? Provide Examples.
2. Define symmetry.

22. Assessment: Online Quiz
3. Encircle symmetric figures while cross out asymmetric figures.
4. Draw the line of symmetry in the following figures:

23. Assessment: Online Quiz
5. Locate the Center of Symmetry in the following:

24. Sources:
Books:
• Oronce, O. and M. Mendoza. Worktext in Mathematics for Third Year High School e-
math:Geometry.
• Buzon, O. et.al. Geometry: Patterns and Practicalities.
• Dilao, S. and J. Bernabe. Geometry:Textbook for Third Year
Online materials:
Youtube, Wikipedia, Google