Theorem of circle;

1, three points that are not on a straight line determine a circle.

2. The vertical diameter theorem divides the chord perpendicular to the chord diameter into two parts, and divides the two arcs opposite the chord into two parts.

(1) bisects the diameter (not the diameter) of the chord perpendicular to the chord and bisects the two arcs opposite to the chord.

(2) The perpendicular line of the chord passes through the center of the circle and bisects the two arcs opposite to the chord.

③ bisect the diameter of an arc opposite to the chord, bisect the chord vertically, and bisect the other section opposite to the chord.

3. The arcs sandwiched between two parallel chords of a circle are equal.

4. A circle is a central symmetrical figure with the center of the circle as the symmetrical center.

5. A circle is a set of points whose distance from a fixed point is equal to a fixed length.

6. The interior of a circle can be regarded as a collection of points whose center distance is less than the radius.

7. The outside of a circle can be regarded as a collection of points whose center distance is greater than the radius.

8. The same circle or the same circle has the same radius.

9. The distance to a fixed point is equal to the trajectory of a fixed-length point, which is a circle with the fixed point as the center and the fixed length as the radius.

10. In the same circle or in the same circle, the isocentric angle has equal arc, chord and chord center distance.

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