2. The line segment connecting any two points on the circle is called chord, and the chord passing through the center of the circle is called diameter.
3. The part between any two points on the circle is called arc, or simply arc. Two endpoints of any diameter of a circle divide the circle into two arcs, and each arc is called a semicircle. Two circles that can overlap are called equal circles. In the same circle or equal circle, arcs that can coincide with each other are called
Equal arc.
A circle is an axisymmetric figure, and any straight line with diameter is its axis of symmetry.
5 bisect the chord perpendicular to its diameter and bisect the two arcs opposite the chord.
6. bisect the diameter of the chord (not the diameter) perpendicular to the chord and bisect the two arcs opposite the chord.
7. We call the angle of the vertex at the center of the circle the central angle.
8. In the same circle or in the same circle, the arcs with equal central angles are equal and the chords are equal.
9. If two arcs are equal in the same circle or equal circle, their central angles are equal and their chords are equal.
10. If two chords are equal in the same circle or equal circle, then their central angles are equal and their arcs are equal.
1 1. The angle whose vertex is on the circle and whose two sides intersect the circle is called the circumferential angle.
12. In the same circle or equal circle, the circumferential angle of the same arc or equal arc is equal, which is equal to half the central angle of the arc.
13. The circumference angle subtended by the semicircle (or radius) is a right angle, and the chord subtended by the circumference angle is a diameter.
14. If all vertices of a polygon are on the same circle, the polygon is called a polygon inscribed in a circle, and the circle is called a circumscribed polygon.
15. In the same circle or equal circle, if two circumferential angles are equal, the arcs they subtend must be equal.
16. Diagonal Complementarity of a quadrilateral inscribed in a circle.
17. point p is outside the circle-d >; R point p is in the circle -d = r point p is in the circle -d
18. Three points that are not on the same straight line determine a circle.
19. You can draw a circle through the three vertices of a triangle. This circle is called the circumscribed circle of the triangle, and 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.
20. Lines and circles have two things in common. At this time, we say that this straight line intersects the circle, and this straight line is called the secant of the circle.
2 1. Lines and circles have only one thing in common. At this time, we say that this straight line is tangent to the circle, which is called the tangent of the circle, and this point is called the tangent point.
22. Lines and circles have nothing in common. At this time, we say that straight lines and circles are separate.
23. straight lines l and o-dr
24. The straight line passing through the outer end of the radius and perpendicular to the radius is the tangent of the circle.
25. The tangent of the circle is perpendicular to the radius of the tangent point.
26. Tangent to the circle through a point outside the circle. The length of the line segment between the point and the tangent point is called the tangent length of the point to the circle.
27. 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.
28. The circle tangent to each side of the triangle is called the inscribed circle of the triangle, and the center of the inscribed circle is the intersection point of the bisectors of the three angles of the triangle, which is called the heart of the triangle.
29. If two circles have nothing in common, they are said to be separated. (Outer and Inner) If two circles have only one common point, they are said to be tangent. (external and internal). If these two circles have two points in common, they are said to intersect.
30. The distance between the centers of two circles is called the center distance.
3 1. We call the center of the circumscribed circle of a regular polygon as the center of the regular polygon, the radius of the circumscribed circle as the radius of the regular polygon, the central angle of each side of the regular polygon as the central angle of the regular polygon, and the distance from the center to one side of the regular polygon as the vertex of the regular polygon.
32. In a circle with radius r, because the arc length corresponding to the central angle of 360 is the circumference of the circle c = 2π r, the arc length corresponding to the central angle n is nπ r =- 180.
33. The figure enclosed by the circular arcs with two radii forming the central angle and the central angle is called a fan.
34. In a circle with a radius of r, the sector area relative to the central angle of 360 is
Is the circular area s = π r?
35. We call the line segment connecting the vertex and any point on the circumference of the cone bottom surface a cone.
The bus.