(1) A Preliminary Understanding of Angle
1. What is an angle?
Through children's observation of some electrical appliances in daily life, it is found that the "horn" is "sharp" and "horn has two straight sides." So we can get the definition of angle.
Definition of an angle: An angle is a figure consisting of a vertex and two sides.
The reference topics are as follows:
The front-line teacher tells you that it is more efficient to learn the second-grade mathematics "Preliminary Understanding of Corner".
The first topic is "Definition of Angle". Write the name of each part in brackets.
The second topic is also the definition of angle. Give five numbers. What are the angles in the five figures?
This question is very representative, and parents can let their children orally say which horns are. Then tell me why some figures are not angles.
There is an edge in the second figure that is not straight, so it is not an angle; The fifth figure has only two straight lines without vertices, so it is not an angle.
It is a good way to let children deepen and consolidate their mastery of knowledge points by oral English.
2. Can you draw a corner?
Method of drawing angle: Starting from one point, draw two straight lines in different directions with a ruler to draw an angle.
Dear children, take out your triangle and draw an edge.
The angle has nothing to do with the length of two sides.
We still learn by examples. Let's look at the picture below.
Title requirements: Compare the relationship between the three groups of angles. What did you find?
The front-line teacher tells you that it is more efficient to learn the second-grade mathematics "Preliminary Understanding of Corner".
I found that "the size of the angle has nothing to do with the length of two sides", which is a knowledge point and a very important test site. Children are not only required to speak, but also to write.
4. Preliminary understanding of right angle, acute angle and obtuse angle.
1. Judgment method of right angle: Take out the triangular ruler and compare it with the right angle of the triangular ruler.
The method of judging right angles by right angles on a triangular ruler: right angles are vertex to vertex, one side to one side and the other side to one side.
2. Method of drawing right angles
(Right-angle drawing is the key and difficult point of this lesson)
Step 1: Draw a point as the vertex of the right angle, and then draw a straight line from this vertex as one side of the right angle;
Step 2: Overlap the right-angle vertex of the triangle ruler with this point, and one right-angle edge of the triangle ruler coincides with this line, and then draw a straight line along the other right-angle edge of the triangle ruler from this point.
Step 3: Mark the right-angle symbol.
3. Oblique and acute angles extending on the basis of right angles.
Oblique angle: Oblique angle is greater than right angle.
Acute angle: acute angle is less than right angle.
From this, we can also draw a conclusion that the angle formed by right angle and acute angle must be obtuse. This picture usually appears in the exam in the form of judgment questions.