2 pie is a multiple of radius and perimeter, so 2 pie times of radius is equal to perimeter, perimeter is 360 degrees, and 2 pie times of equivalent replacement radius is equal to 360 degrees. More importantly, the meaning of pie refers to the relationship between radius and perimeter, which has no other use, so pie omits the process of explanation, which is better than the process of explanation. As for the length of the radius, it does not affect the proportion of the circumference, that is, the radius and the pie are not contradictory. Therefore, "assuming the radius is 2, the four factions" are two 2 factions, which are the proportional perimeters of two circles, and the equivalent substitution is equal to 720 degrees, that is, the faction represents 180 degrees.