The chord passing through the center of the circle is called the diameter. 3. The part between any two points on the circle is called arc, the arc larger than semicircle is called upper arc, and the arc smaller than semicircle is called lower arc. 4. Two endpoints of any diameter of a circle divide the circle into two arcs, and each arc is called a semicircle. 5. As shown in the figure, the vertex of ∠AOB is at the center of the circle, and the angle of the vertex at the center of the circle like this is called the central angle. Its axis of symmetry is any straight line passing through the center of the circle. 2. bisect the chord perpendicular to the diameter of the chord and bisect the two arcs it faces. The diameter (not the diameter) of bisecting a chord is perpendicular to the chord and bisects the two arcs it faces. 3. In the same circle or in the same circle, the arcs with equal central angles are equal and the chords are equal. In the same circle or in the same circle, if two arcs are equal, then the central angles they face are equal. If two chords are equal, then their central angles are equal and their arcs are equal. 4. In the same circle or equal circle, the central angle of the same arc and equal arc is equal, which is equal to half of the central angle of this arc. The central angle (or diameter) of a semicircle is a right angle, and the chord of 90 is the diameter. 24.2 knowledge summary,
Let the radius of ⊙O be r and the distance from point P to the circle be d,
Then there is: point P is outside the circle.
d & gtr
Point p is on the circle.
D=r point p is in the circle.
D<r defines 1.
Position relationship between point and circle
2.
You can make a circle through the three vertices of a triangle, which is called the circumscribed circle of the triangle.
The center of the circumscribed circle is the intersection of the perpendicular lines of the three sides of the triangle, which is called the center of the triangle.
3. The positional relationship between the straight line and the circle: the straight line L intersects with ⊙ O.
D<r, the straight line L and ⊙O are tangent.
d=r，
The straight line l and ⊙O are separated.
d & gtr.
4.
Tangent line of a circle, tangent length, inscribed circle.
5. The positional relationship between circles
Outward separation
D>R 1+r2 circumscribed
D=r 1+r2 intersection
│r 1-R2│& lt； D<R 1+r2 cutting
D=│r 1-r2│ inclusive.
0≤d & lt； │r 1-r2│ (where d=0, two circles are concentric) 1. Theorem 1.
Three points that are not on the same straight line determine a circle.
Judgment theorem of tangent;
The straight line passing through the outer end of the radius and perpendicular to the radius is the tangent of the circle.
Property theorem of tangent;
The tangent of a circle is perpendicular to the radius of the tangent point.
Tangent length theorem;
Two tangents of a circle can be drawn from a point outside the circle, and their tangents are equal in length. The connecting line between this point and the center of the circle bisects the included angle of the two tangents.