1. LESSON 2 UNDEFINED TERMS

2. In Geometry, there are 3 undefined terms: points, lines, and planes. We can give descriptions of these three terms. We also use these terms to help us write definitions of other terms such as segment, or ray

3. WHY THESE TERMS CALLED UNDEFINED? It is because they can only be defined circularly which means in terms of each other or in terms of themselves.

4. POINT A point is usually represented by a dot on a piece of paper. It is so small that it can never be measured because it has no dimensions at all.

5. - It shows location. - It is named by one capital letter. A BC A, B, and C are COLLINEAR POINTS

6. COLLINEAR POINTS - Points that lie on the same line. NONCOLLINEAR POINTS - Points that do not lie on the same line.

7. Examples COLLINEAR POINTS - B, A, L, K - S, M, K - Q, M, ? - T, ?, D S M Q B D H T K LA

8. Examples NONCOLLINEAR POINTS - B, A, M, K - D, M, K - Q, M, ? - T, ?, D S M Q B D H T K LA

9. LINES - A line is always straight and travels forever (INFINITE) in two directions. - has no width BUT IT HAS length( which is infinite).

10. ILLUSTRATION A BC The opposite arrow indicates that it extends indefinitely in opposite direction.

11. Lines can be named in 2 ways: 1. by its endpoints. For example, in the figure, A BC Line AB or AB. Or Line BA or BA Line AC or AC. Or Line CA or CA

12. 2. Lines are also named with lowercase letters or a single lower case letter A BC The line above can be named also as line m instead of line AB or line AC. m

13. A B D WHAT HAPPEN IF YOU CUT THE LINE SHOWN BELOW AT POINT B and C? WHAT ARE THE NEW FIGURES FORMED? C

14. SUBSETS OF A LINE A B DC A B C D B C RAY SEGMENT

15. SUBSETS OF A LINE B Definition : -is a straight line segment which is part of the straight line between two points. -The points on each side of the line segment are referred to as the end points C SEGMENT

16. SUBSETS OF A LINE B Segment is named by its endpoint. Segment BC or segment CB. In symbol, BC or CB C SEGMENT

17. SUBSETS OF A LINE A Definition : -A ray is the part of the line which consists of the given point and the set of all points on one side of the end point. -The ENDPOINT is the starting point and the ARROW determine the direction of the ray. B

18. SUBSETS OF A LINE A In writing, ray BA but not ray AB. ray CD but not ray DC. D B C RAY

19. SUBSETS OF A LINE A In symbols, BA (reads as ray BA) CD (reads as ray CD) D B C RAY

20. PLANE A plane is often represented by a FLAT SURFACE. These 'plane' surfaces are used to connect any two or more points on a straight line.

21. THE FLOOR

22. THE WALL AND THE CEILING

23. PICTURE FRAME

24. PLANE In naming, -Named by 3 distinct points which are not collinear. -For example, plane BDC. D B C

25. β PLANE or -Single greek alphabet. -For example, Plane β

26. β PLANE -A plane has no thickness and edges. - has length and width.

27. ASSESSMENT