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. [3]

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.

Flat angle: The angle equal to 180 is called flat angle.

Bending angle: the value greater than 180 and less than 360 is called bending angle.

Lower angle: more than 0 and less than 180 is called lower angle, and acute angle, right angle and obtuse angle are all lower angles.

corner

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.

Zero degree angle: an angle equal to zero degree.

6 Special angle

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.

Adjacent complementary angles: two angles have a common edge, and their other edge is an opposite extension line. Two angles with this relationship are adjacent complementary angles.

Internal angle: two parallel straight lines are cut by a third straight line, if both angles are on two straight lines.

Internal angle, ipsilateral internal angle, congruent angle

Inside, and on both sides of the third straight line, then such a diagonal line is called alternating inner angle. Such as: ∠ 1 and ∠6, ∠2 and ∠5.

Inner angle on the same side: two angles are on the same side of the dividing line, and between the two dividing lines, a diagonal with this positional relationship is the inner angle on the same side. Such as: ∠ 1 and ∠5, ∠2 and ∠6.

Coincidence angle: the two angles are on the same side of the section line and the same side of two straight lines respectively. A pair of diagonals with this positional relationship are called coincidence angles: ≈ 1 and ∠8, ∠2 and ∠7.

External dislocation angle: two straight lines are cut by a third straight line to form eight angles. If both angles are outside and on both sides of the secant, then such a pair of angles is called the external dislocation angle. For example: ∠4 and ∠7, ∠3 and ∠8

Exterior angle on the same side: two angles are on the same side of the dividing line, and outside the two dividing lines, a pair of angles with this positional relationship are exterior angles on the same side. Such as: ∠4 and ∠8, ∠3 and ∠7.

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