A bicycle is like a cow with two horns on its head. The two handlebars are the two corners of the bicycle, which grow on the head of the bicycle to protect the safety of the bicycle and master the direction of the bicycle. In the case of a single vertex, assuming that there are n rays including the outermost two rays, the number of angles of large and small * * * is:1+2+3+...+(n-2)+(n-1).

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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 zero 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.