An angle consists of two straight lines (or line segments), and the included angle formed by the two straight lines (or line segments), whether acute, obtuse, flat or rounded, should be regarded as an angle.

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.

Extended data:

In the two-dimensional Cartesian coordinate system, the angle is generally based on the positive direction of the X axis. If it rotates in the positive direction of the Y axis, its angle is positive, and if it rotates in the negative direction of the Y axis, its angle is negative. If the two-dimensional Cartesian coordinate system is also the X-axis to the right and the Y-axis to the right, then the counterclockwise rotation corresponds to a positive angle and the clockwise rotation corresponds to a negative angle.

Generally speaking,? The angle θ is the same as the angle obtained by subtracting θ from a circle. Like what? 45 and 360? 45 (= 3 15) is equivalent, but it is only applicable to the case of relative position expressed by angle, not the concept of rotation. Spin? 45 is different from 3 15.

In three-dimensional geometry, there is no absolute definition of clockwise and counterclockwise, so when defining positive and negative angles, reference datum planes should be listed, usually based on a vertex passing through the angle and a vector perpendicular to the plane of the angle.

In navigation, the guidance is based on the north, and the positive direction is clockwise, so the guidance 45 corresponds to the northeast direction. The direction has no negative value, and the corresponding northwest direction is 3 15.