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### Lesson 1.2

Intro to Geometry

I can understand basic geometric terms and postulates.

1. Points

- Points do not have actual size.
- How to Sketch:

Using dots

- How to label:

Use capital letters

A

B

2. Postulates

- An accepted statement of fact.

3. Line POSTULATE – Through any two points there is exactly ONE line

- Lines extend indefinitely and have no thickness or width.
- How to sketch : using arrows at both ends.
- How to name: 2 ways

(1) small script letter – line n

(2) any 2points on the line -

- Never name a line using three points -

n

A

B

C

4. Segment

A part of a line that consists of two endpoints and all the points in between them.

How to name: by 2 endpoints

A

B

C

5. Ray

- A part of a line that consists of one endpoint and all the points to one side of that endpoint.

A

B

C

How to name: 2 points with ENDPOINT FIRST

Not like this…

6. Collinear Points

- Collinear points are points that lie on the same line.

C

A

A

B

C

B

Non collinear

Collinear

7. Planes POSTULATE – Through any 3 non-collinear points there is exactly ONE plane

- A plane is a flat surface that extends indefinitely in all directions.
- How to sketch: Use a parallelogram (four sided figure)
- How to name: 2 ways

(1) Capital script letter – Plane M

(2) Any 3 non collinear points in the plane - Plane: ABCor BCA or BAC, etc.

A

M

B

C

Other planes in the same figure:

Any three non collinear points determine a plane!

Plane ACG

Plane ACH

Etc.

8. CoplanarObjects

Coplanar objects (points, lines, etc.) are objects that lie on the same plane.

Are the following points coplanar?

A, B, C ?

Yes

A, B, C, F ?

No

H, G, F, E ?

Yes

E, H, C, B ?

Yes

A, G, F ?

Yes

C, B, F, H ?

No

9. Intersection of Two Lines POSTULATE

The intersection of two lines is a point.

m

Line m and line n intersect at point P.

P

n

10. Intersection of Two Planes POSTULATE

The intersection of two planes is exactly ONE line.

B

P

A

R

Plane P and Plane R intersect at the line

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