The common forms of invisible circle are as follows: one is diagonal complementarity, the other is four-point * * * circle; The second is to set the chord and angle, and the point is on the circle; The third is fixed point and fixed length, and the trajectory is round. The specific themes are folding, rotation and angle invariance.
The conditions that can form an invisible circle mainly include the following.
An invisible circle with a fixed point and a fixed length. Wherein a circle is made with a fixed point as the center and a fixed length as the radius.
The fixed angle of a fixed line segment (fixed angle means that the position of the angle is not fixed, but it can move, and the degree of the angle remains the same in the process of moving around the fixed line segment, that is, the fixed angle) constitutes an invisible circle.
A chord with a fixed length is a circle, and the fixed angle of a fixed chord is a circumferential angle. If this condition is met, an invisible circle will be formed.
An invisible circle composed of diagonally complementary quadrangles. The theoretical basis of this example is "diagonal complementarity of quadrangles inscribed in a circle".
Equiangular pairs on the same side form an invisible circle.