Type of angle: the size of the angle has nothing to do with the length of the side; The size of an angle depends on the degree to which both sides of the angle are open. The bigger the opening, the bigger the angle. Conversely, the smaller the opening, the smaller the angle. In dynamic definition, it depends on the direction and angle of rotation. 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. An angle measuring system in degrees, minutes and seconds is called an angle system. In addition, there are secret system, arc system and so on.

Acute angle: An angle greater than 0 and less than 90 is called an acute angle.

Right angle: An angle equal to 90 is called a right angle.

Oblique angle: an angle greater than 90 and less than180 is called obtuse angle.

Boxer: An angle equal to 180 is called a boxer.

Excellent angle: more than180 and less than 360 is called excellent angle.

Bad angle: it is called bad angle when it is greater than 0 but less than 180. Acute angle, right angle and obtuse angle are all bad angles.

Fillet: An angle equal to 360 is called a fillet.

Negative angle: the angle formed by clockwise rotation is called negative angle.

Positive angle: the angle of counterclockwise rotation is positive angle.

Angle 0: An angle equal to zero.

Complementary angle and complementary angle: if the sum of two angles is 90, it is complementary angle, and if the sum of two angles is180, it is complementary angle. The complementary angles of equal angles are equal, and the complementary angles of equal angles are equal.

Inverse vertex angle: When two straight lines intersect, there is only one common vertex, and both sides of the two corners are opposite extension lines. These two angles are called antipodal angles. Two straight lines intersect to form two pairs of vertex angles. The two opposite angles are equal.

There are also many kinds of angle relationships, such as internal dislocation angle, congruent angle and internal angle of the same side (in the three-line octagon, it is mainly used to judge parallelism)!