(1) Make students understand the concept and characteristics of parallelogram and draw the height of parallelogram.

(B) enable students to master the relationship between rectangles, squares and parallelograms.

(3) Further improve students' abilities of observation, comparison and drawing.

Teaching emphases and difficulties

Understanding and mastering the definition and characteristics of parallelogram and drawing the height of parallelogram are the key points of teaching; It is difficult to understand the relationship between rectangle, square and parallelogram.

Teaching process design

Review preparation

We have learned some geometric figures. Let's observe the characteristics of these figures. (projection)

On the basis of making it clear that they are all surrounded by four line segments, it is concluded that the figure surrounded by four line segments is quadrilateral.

Question: What quadrilaterals have we learned?

The quadrangles I have studied are rectangle, square and parallelogram. )

Can you give an example of which objects have parallelogram surfaces?

The teacher shows the wall chart, so that the students can initially perceive the parallelogram.

We have a preliminary understanding of parallelogram, so what is parallelogram? What are its characteristics? This is the subject we are going to study today.

Learn a new course

1. Understanding parallelogram

Definition of.

First show a set of graphics:

What are these shapes? What are their characteristics?

① Hands-on measurement.

Name a student on the blackboard and check it with a triangle.

The rest of the students use a triangle to check the opposite sides of 15 1 page.

Then measure the length of each group of opposite sides with a ruler.

② abstract generalization.

According to your measurement results, can you tell me what a parallelogram is?

Let the group discuss first (it can be said that each group of opposite sides of the parallelogram is equal, or it can be said that each group of opposite sides of the parallelogram is parallel), and then let the students who measure on the blackboard say the results of inspection and measurement, thus leading to the exact meaning of the parallelogram.

Two groups of parallelograms with parallel opposite sides are called parallelograms.

The teacher stressed that as long as each group of opposite sides of a quadrilateral is parallel, it can be determined that its two groups of opposite sides are equal, so the definition of a parallelogram is "a quadrilateral with two groups of opposite sides parallel respectively".

Feedback: Which of the following figures is a parallelogram? (projection)

Students have studied triangles, which have stable characteristics. What are the characteristics of parallelogram?

(1) teacher's demonstration.

The teacher took a rectangular wooden frame, grabbed the two opposite corners of the rectangle with both hands and pulled it in opposite directions. Observe what has happened to the opposite sides. What shape is it painted? What hasn't changed?

The students made it clear that the lengths of the two groups did not change, and they all became parallelograms, and the four right angles became acute angles and obtuse angles.

(2) Hands-on operation.

Students do it themselves, draw the prepared rectangular frame into a parallelogram, and measure whether the two groups of opposite sides are parallel.

(3) Summarize the characteristics of parallelogram.

According to the experiment and measurement just now, guide the students to conclude that the parallelogram is unstable.

2. The characteristics of parallelogram.

Blackboard book)

(4) comparison.

The triangle is stable and not easy to deform. Parallelogram is different from triangle, which is easy to deform, that is, unstable.

This instability is widely used in practice. Can you give some practical examples? (such as protective net of garage, sliding door, scale, etc.). )

3. Learn the base and height of parallelogram.

(1) Know the base and height of the parallelogram.

Show:

The teacher explained while demonstrating:

Draw a vertical line from one point on one side of the parallelogram to the other. The line segment between this point and the vertical foot is called the height of the parallelogram. This opposite side is called the base of the parallelogram.

(2) Find the corresponding bottom and height.

Display: (Projection)

Look at the picture. How high is it? Which line segments are at the bottom of them?

Let the students make it clear: draw the height from point B, and its bottom is CD; Draw the height from point D, and the bottom is BC.

(3) Draw the height of the parallelogram.

The students have learned how to draw the height of a triangle. The method of drawing the height of parallelogram is the same. They all use the method of drawing the perpendicular of a known straight line from a point outside the straight line. You can draw the height from any point on an edge to its opposite side, but usually you draw the height from the vertex of an angle to its opposite side. The height here should be drawn as a parallelogram, and it is not required to draw the height on the extension line of the bottom.

Students begin to draw the height: 152 page "Do it".

4. Teach the relationship between rectangle, square and parallelogram.

The teacher used a rectangular frame to pull the sides of the rectangle to make it into different parallelograms. They can also change the parallelogram into a rectangle and compare the similarities and differences between the rectangle and the parallelogram.

& gt

Guide the students to make it clear that the same point is parallel to two opposite sides, so the rectangle also has the characteristics of parallelogram and belongs to parallelogram. The difference is that all four corners of the rectangle are right angles, so the rectangle is regarded as a special parallelogram.

Compare the similarities and differences between squares and parallelograms.

Guide the students to make it clear that a square is also two groups of special parallelograms with parallel opposite sides, and all four corners are right angles. Because both a rectangle and a square have two groups of parallel opposite sides, four corners are the same point at right angles, and a square has four equal sides, a square can also be regarded as a special rectangle.

The relationship between these three graphs can be expressed by set graph.

(3) Integrated feedback

1. What is a parallelogram? What are its characteristics?

& gt

Guide the students to make it clear that the same point is parallel to two opposite sides, so the rectangle also has the characteristics of parallelogram and belongs to parallelogram. The difference is that all four corners of the rectangle are right angles, so the rectangle is regarded as a special parallelogram.

Compare the similarities and differences between squares and parallelograms.

Guide the students to make it clear that a square is also two groups of special parallelograms with parallel opposite sides, and all four corners are right angles. Because both a rectangle and a square have two groups of parallel opposite sides, four corners are the same point at right angles, and a square has four equal sides, a square can also be regarded as a special rectangle.

The relationship between these three graphs can be expressed by set graph.

(3) Integrated feedback

1. What is a parallelogram? What are its characteristics?

2. Draw the height in the picture below and point out its bottom.

3. Draw two different heights in the picture below.

4. Talk about the relationship between parallelogram, rectangle and square.

(4) homework

Omitted)

Description of classroom teaching design

On the basis of students' initial perception of parallelogram, this lesson establishes a clear concept for students through intuitive demonstration and operation practice.

The new lesson is divided into four parts.

First, let the students check three parallelograms with different shapes by the method of checking parallel lines mentioned above, and then measure the length of each group of opposite sides with a ruler, so that the students can find the characteristics of parallelograms from practice and summarize the definition of parallelograms abstractly.

Secondly, through teachers' demonstration and students' actual operation, it is found that the characteristic of parallelogram is instability.

Then know the base and height of the parallelogram and draw the height.

Finally, by comparing the similarities and differences of rectangles, squares and parallel lines, the relationship between them is clarified: squares are special rectangles, and rectangles and squares are special parallelograms, which are represented by set diagrams.

In teaching or practice, we should not only attach importance to intuitive demonstration and use comparative method, but also strengthen hands-on operation, measure and draw a picture, so that students can gain knowledge and improve their ability in practice.

blackboard-writing design

parallelogram

A figure surrounded by four line segments is called a quadrilateral.

Two groups of parallelograms with parallel opposite sides are called parallelograms.

Features: unstable.

Draw two different heights.