A polygon with equal sides and equal angles is called Regular polygon (polygon: Edge number is greater than be tantamount to 3). The center of a circle is called a Regular polygon center. The length of the line between the center and Regular polygon vertices is called radius. The distance between the center and the side is called the distance between the sides. Regular polygon symmetry axis - odd number side: connect one vertex and the vertex opposite the middle point, that is, the axis of symmetry; Even number side: connected to the opposite two sides of the midpoint, or connected to the opposite two vertices, both are axes of symmetry. The Edge number of a positive n-sided shape is the symmetry bar number is N.