Angles can be divided into acute angle, right angle, obtuse angle, right angle, rounded corner, negative angle, positive angle, upper angle, lower angle and 0 angle, which are 10 respectively. These angles can be expressed or marked in the following four ways. (three-letter method, one-letter method, number method, Greek alphabet method)

Method 1: Use three uppercase English letters, such as ∠AOC (the vertex is written in the middle, indicating that the angle is the angle between ray OA and line segment OC).

Method 2: Use capital English letters, for example: ∠O (indicating that the vertex of the angle is point o).

Method 3: Use numbers to represent it, such as ∠ 1, ∠2, ∠3 (commonly used in mathematical problems to mark abbreviations on drawings).

Method 4: Use 1 Greek letter, for example: ∠ β.

Extended data

The correct use of angle representation can make the expression accurate when solving problems, facilitate the recognition of figures and help improve the rigor of problem-solving ideas. If the angle is not properly expressed, it may lead to unclear or incorrect expression, affect the choice of angle, make the angle to be expressed not correspond to the actual angle, and cause misunderstanding. Therefore, it is necessary to determine the differences between the four expressions.

The applications of the above four representations are different.

1. Any angle can be represented by three uppercase English letters, but the middle letter must be the vertex of the angle;

2. When a vertex only corresponds to an angle, the other three methods can also be used to represent the angle;

3. When two or more angles have a vertex, that is, a vertex corresponds to several angles, then an angle cannot be represented by a capital letter.

4, when the graphics are more complex, the number of Angle is more, can't intuitive identification, should use Greek letters or numbers to mark.

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