In junior high school, we call the figure surrounded by two rays an angle, which is divided into 0~ 180 degrees, and define acute angle, obtuse angle, right angle, right angle and 360-degree fillet.

But in reality, we can often see situations where the angle exceeds 360 degrees, such as gymnastics turn 1080 degrees (three turns). When driving, we sometimes have to distinguish between turning left 45 degrees and turning right 45 degrees, so we should introduce the concept of negative angle like introducing negative numbers.

So we redefined the diagonal,

In this way, the angle greater than 360 degrees is completed, and the concept of negative angle is directly introduced. ...

The figure formed by the rotation of a ray around its endpoint is called an angle, this ray is called the starting edge of the angle, the edge corresponding to the rotation position is called the ending edge of the angle, and this common endpoint is called the vertex of the angle.