1. 1.2 Points, Lines, and Planes

2. There are three undefined terms in geometry:
What is a definition?
Known words used to describe a new word
Undefined terms – are terms not formally defined.
There are three undefined terms in geometry:
1. Point 2. Line 3. Plane

3. Point 1. A location in space.
2. Has no dimension (no length, no width, no depth).
3. Usually represented by a dot.
4. Named using one capital letter.

4. Point
For example: ●B

5. Line
A series of points that extends in opposite directions without end.
One-dimensional (length).
Has an arrowhead on each end representing the fact that it goes on forever.
Always straight.
Named with a lowercase script letter or by 2 points on the line

6. Line For example: Can be called: Line l Line AB or AB l Line BA or BA

7. Plane
A flat surface that extends forever in two dimensions (length & width).
Contains infinitely many points and lines.
Usually represented by a four-sided figure.
Named with a capital script letter or 3 points on the surface of the plane

8. Plane For example: Can be named: Plane W
Plane ABC, plane BCA, plane CBA, etc. A W C B

9. More Definitions Collinear points –
points that can lie on the same line.

10. More Definitions
Noncollinear points – D

11. More Definitions Coplanar points –
points that can lie on the same plane.

12. More Definitions
Noncoplanar points – A D

13. More Definitions
Equidistant – equally distant

14. More Definitions Intersect –
Two or more figures intersect if they have one or more points in common.
Intersection –
All points or sets of points the figures have in common.

15. When a line and a point intersect, their intersection is a point.B

16. When 2 lines intersect, their intersection is a point.

17. When 2 planes intersect, their intersection is a line.

18. When a line and plane intersect, their intersection is a point.

19. Questions???

20. Classify each statements as true or false
REMOTE TIME !
Classify each statements as true or false

21. Question 1
PF ends at P

22. Question 2
Point S is on an infinite number of lines

23. Question 3
A plane has no thickness

24. Question 4
Collinear points are coplanar

25. Question 5
Planes have edges

26. Question 6
Two planes intersect in a line segment

27. Question 7
Two intersecting lines meet in exactly one point

28. Question 8
Points have no size

29. Question 9
Line XY can be denoted as XY or YX.

30. Horizontal Planes – Ceiling and Floor
Horizontal Planes – Two sides horizontal and no sides vertical

31. Vertical Planes – Walls
Vertical Planes – two sides are vertical

33. Vertical line l intersects a horizontal plane M at point O
Group Practice
Vertical line l intersects a horizontal plane M at point O

34. Horizontal plane Q and vertical plane N intersect
Group Practice
Horizontal plane Q and vertical plane N intersect

35. Group Practice
Point P is not in Plane N. Three lines through point P intersect N in points A, B, and C.

36. True or False
All points on a line are coplanar

37. True or False
A line has one endpoint

38. True or False
A point is named by a capital letter.

39. True or False
Two lines intersect in two points.

40. True or False
The edge of a plane is a line.