In the second grade, students have not been exposed to the concept of radian. Senior two students will only use simple methods to draw angles, draw arcs on rays, and use compasses to determine the size of angles. It can help students understand and practice the concept of angle, and lay a foundation for the subsequent study of geometry knowledge. In mathematics and physics, radian is the unit of measurement of angle. It is a unit derived from the international system of units, abbreviated as rad.