"Points and Lines" PPT Courseware 2

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"Points and Lines" PPT Courseware 2

Observe the faces of this cuboid. What do you get when the faces intersect?

Point representation:

Use a capital letter. For example: point A, point B.

What figure is obtained by connecting point A and point B?

Representation of line segments:

Method 1: Use two uppercase letters indicating the endpoint (in no order).

For example: line segment AB, line segment BA.

Method 2: Use a lowercase letter. For example, line segment a.

A figure formed by a line segment extending infinitely in one direction is called a ray

Representation of rays:

Method 1: Use the capital letter representing the endpoint and the letters of any other points (the capital letter representing the endpoint must be written first).

Thinking: Are ray AB and ray BA the same?

Method 2: Use a lowercase letter. For example, ray a.

A figure formed by extending a line segment infinitely in both directions is called a straight line

Straight line representation:

Method 1: Use two capital letters to represent any two points (in no order).

For example: straight line AB, straight line BA.

Method 2: Use a lowercase letter. For example, straight line a.

Exercise 1

1. Extending a line segment infinitely in one direction forms __, and extending it infinitely in two directions forms ____.

2. The light emitted by the flashlight can be regarded as a __________

3. As shown in the figure, the line segments in the figure can be expressed as line segments _________ or as line segments _________

4. Which of the following means that rays PA and PB are the same ray ( )

5. Please extend the line segment AB in the figure below to the ray with A as the endpoint.

6. Please extend the line segment AB in the figure below to both sides to obtain rays with A and B as endpoints respectively.

7. In the following example,

①A thin line pulled very tightly is a straight line

②Half of the straight line is a ray;

③ Line segment AB and line segment BA represent the same line segment;

④Ray AB and ray BA represent the same ray.

The correct number is ()

A.1 B.2 C.3 D.4

Draw a picture:

1. Draw a straight line through point A: How many straight lines can you draw?

Conclusion: There are countless straight lines passing through a point

2. Draw straight lines through two points A and B. How many straight lines can you draw?

Conclusion: There is a straight line through two points, and there is only one straight line

Abbreviated as: two points determine a straight line

Exercise 2.

1. To nail a wooden strip to the wall, at least --- nails must be nailed. The principle is ---

2. When planting trees on the roadside, you usually set up stakes and lines at both ends of the road, and then plant trees along the line. The reason is————

3. In the same plane, there are four points A, B, C, and D. Every three points are not on the same straight line. How many straight lines can be drawn through every two points?

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Update Time: 2024-11-22

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