"Magnification and reduction of graphics" similar graphics PPT courseware 3

Description

"Magnification and reduction of graphics" similar graphics PPT courseware 3

learning target

1. Understand the similarity figures and related concepts, and understand that the ratio of the distance between any pair of corresponding points on the similarity figures to the similarity center is equal to the similarity ratio.

2. Able to enlarge or reduce a figure using the method of positioning like figures.

3. Be able to use the properties of position-like figures to solve practical problems, develop students' awareness of mathematical applications, and further cultivate students' hands-on ability.

Review the past and learn the new

What are similar polygons?

What is the similarity ratio of similar polygons?

What are some ways to determine if two triangles are similar?

New course introduction

As shown in the figure, it is the working principle diagram of the slide projector. If the size of the slide is 3.5cm×3.5cm, the size of the screen for projection is 2m×2m. If the light source is 20cm away from the slide, how far should the screen be from the slide? The image just fills the entire screen.

Knowledge explanation

The following set of pictures are graphics with the same shape. Take point A on picture ①. Does the line connecting it to the corresponding point B on another picture (such as picture ②) pass through the center of lens P? Change the picture Try other places, are there any similar conclusions?

Definition: If two figures are not only similar figures, but also the straight lines of each set of corresponding points pass through the same point, then such two figures are called similarity figures, and this point is called the similarity center. The similarity ratio at this time is also called The position is similar.

Track training

As shown in the figure, △OCD and △OAB are similar figures. Are AB and CD parallel? Try to explain why.

Parallel, the reason is: △OCD∽△OAB→∠OCD=∠OAB→AB∥CD

Choose a figure you like, use a rubber band to enlarge the figure to enlarge the known figure to a certain proportion, and try to explain the reason.

Practice in class

1. Is the following statement correct? Why?

(1) Take points D and E on the sides AB and AC of △ABC respectively, so that DE∥BC, then △ADE is the reduced figure of △ABC;

(2) Take points D and E on the extension lines of sides AB and AC of △ABC respectively, so that DE∥BC, then △ADE is the enlarged figure of △ABC;

(3) Take points D and E on the reverse extension lines of sides AB and AC of △ABC, so that DE∥BC, then △ADE is the reduced figure of △ABC;

2. The vertex coordinates of △ABC are A(2,2), B(4,2), and C(6,4). Try to reduce △ABC so that the ratio of the reduced △DEF to the corresponding side of △ABC is 1:2.

3. The three sides of △ABC can be reduced to their original values ​​according to the following method: As shown in the figure, take any point O, connect AO, BO, CO, and take their midpoints D, E, F; the three sides of △DEF are △ABC corresponds to 1/2 of the three sides.

In fact, △ABC and △DEF are similar figures.

Summary of this lesson

Through the study of this class, we need to master:

1. Similar polygons: If two figures are not only similar, but also the straight lines of each set of corresponding vertices pass through the same point, then such two figures are called similarity figures, and this point is called the similarity center. At this time, the similarity ratio Also called position similarity ratio.

2. Properties of the similarity ratio: The ratio of the distances between any pair of corresponding points on the similarity figure to the center of the similarity is equal to the similarity ratio.

3. How to create positional images (enlargement and reduction; upright and inverted images).

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For more information about the PPT courseware "Enlarging and Reducing Similar Figures and Figures", please click the Enlargement and Reduction of Similar Figures PPT Figures ppt tab.

"Magnification and reduction of graphics" similar graphics PPT courseware 2:

"Enlarging and Reducing Figures" Similar Figures PPT Courseware 2 Review and Thinking What are similar polygons? What is the similarity ratio of similar polygons? What are some ways to determine if two triangles are similar? Do you still remember the method of using rubber bands to enlarge graphics on page 116 of the third section of this chapter?

"Magnification and reduction of graphics" similar graphics PPT courseware:

Review and Reflection of Similar Figures PPT Courseware "Enlarging and Reducing Figures" What are similar polygons?

What is the similarity ratio of similar polygons? What are some ways to determine if two triangles are similar? Do you still remember the use of rubber bands to enlarge graphics on page 104 of the third section of this chapter?

"Magnification and reduction of graphics" Transformation and position determination of graphics PPT courseware 3:

"Enlarging and Reducing Graphics" Transformation and Position Determination of Graphics PPT Courseware 3 These three sets of pictures have the same shape but different sizes. Like this: the shape is the same, but the figure becomes larger, which is called enlargement of the figure. The shape is the same, but the figure becomes smaller, which is called the reduction of the figure. The left picture is long (..

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Update Time: 2024-09-09

This template belongs to Mathematics courseware Beijing Normal University eighth grade mathematics volume 2 industry PPT template

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