Knowledge points of "angle measurement" in the first volume of fourth grade mathematics published by People's Education Press
1. straight line, ray, angular straight line: a straight line extending infinitely to both ends, with no points.
Ray: it can be like a line extending in one direction, and the ray has an endpoint.
Line segment: a line that cannot be extended. A line segment has two endpoints.
Angle:
A figure composed of two rays with a common endpoint is called an angle.
This common endpoint is called the vertex of the angle, and these two rays are called the two sides of the angle.
2. The connection and difference between straight lines, rays and line segments.
1) Both lines and rays can extend indefinitely, so the length cannot be measured.
2) The length of the line segment can be measured.
3) A line segment has two endpoints, a straight line has no endpoint, and a ray has only one endpoint.
3. The characteristics of angle
A corner has a vertex and two sides, as shown in the figure below.
The angle is usually represented by the symbol "∞". 4. Comparison of angles:
The unit of measurement of angle is "degree", and the symbol is "degree". The semicircle is divided into 180 equal parts, and the angle of each equal part is l degrees. Note that it is 1. Measure the angle with a protractor, as shown in the following figure.
Measurement method:
Pay attention to the alignment of measuring angles:
The center of the protractor is aligned with the vertex of the angle;
The 0 scale line of the protractor is aligned with one side of the corner.
After the two are aligned, the other side of the angle faces the scale line several times, and this angle is several degrees.
Look at the scale to distinguish the inner and outer rings. Here I'll teach you a little trick:
Distinguish the inner and outer rings, and follow the scale of 0;
The scale of 0 in the outer ring depends on the scale of the outer ring.
The scale of 0 in the inner ring depends on the scale of the inner ring.
Keep it in mind and never forget it.
note:
The size of the angle has nothing to do with the length drawn on both sides of the angle. The size of the angle depends on the size of both sides. The bigger the fork, the bigger the angle.
5. Classification of angles:
Acute angle < 90, right angle = 90, 90 () >; ()& gt()& gt( )。
5. 1 fillet is equal to () flat angle.
Second, choose.
1. 10:30, the angle between the minute hand and the hour hand is ().
A. obtuse angle B. right angle C. acute angle
2. The angle that two acute angles can form cannot be ().
A. acute angle B. right angle C.
3. Look at an angle of 8 degrees with a magnifying glass of 10 times. The degree of the angle you see is ().
18 degrees C.8 degrees
4. The angle that is 92 degrees smaller than the right angle is ().
A. obtuse angle B. right angle C. acute angle
You can spell the angle of () with a pair of triangular rulers.
360 degrees, 15 degrees, 190 degrees.
Step 3 judge.
At 1.9: 30, the angle between the hour hand and the minute hand is a right angle. ( )
2. The length of a straight line is10m. ( )
3. Two line segments can form an angle. ( )
The sum of two acute angles must be a right angle. ( )
The sum of two boxers must be rounded. ( )
Draw an angle of 20 degrees and 175 degrees with a protractor.
Draw angles of 15 degree and 150 degree with a triangular ruler.
Reference answer
One.
1.2, none, 1
2. Light, Vertex and Edge
3. Boxer corner
4. fillet >; Flat angle > oblique angle > right angle > acute angle
5.2
Two.
Civil Aviation Administration of China
Three.
× × × × √
Four or five omissions
Three-person education edition fourth grade first volume mathematics "angle measurement" exercise.
Four-person education edition, fourth grade, the first volume of mathematics "angle measurement" exercises.
First, fill in the blanks.
(1) leads to two rays from a point, and the () is called (). These two sides () are called angles, which are usually represented by the symbol ().
(2) The greater the angle between the two sides, the greater the angle of the fork (). The size of the angle has nothing to do with ().
(3) The unit of measurement of the angle is (), with the symbol (). The size of the angle is measured by ().
(4) When measuring an angle, the center of the protractor coincides with (), the zero scale coincides with (), and the scale on the protractor opposite to the other side of the angle is () of this angle.
⑤ The angle of () is called acute angle; The angle of () is called obtuse angle; The right angle is () degrees.
At 6.6 o'clock, the hour hand and the minute hand on the clock face form an angle of () degrees, which is called () angle.