Characteristics of roundness
The same circle has countless radii, all of which are equal in length.
The same circle has countless diameters, all of which are equal in length.
The radius of the same circle is 0/2 of the diameter of 65438+, and the diameter is twice the radius.
The line segment with both ends on the circle has the largest diameter.
The size of a circle is determined by its radius, and its position is determined by its center.
A circle is an axisymmetric figure, and its axis of symmetry is an arbitrary straight line passing through the center of the circle. A circle is also a central symmetric figure, and its symmetric center is the center of the circle.
Theorem of Vertical Diameter of a Circle
The diameter perpendicular to the chord bisects the chord and the two arcs it faces.
The perpendicular bisector of the chord passes through the center of the circle and bisects the two arcs opposite to the chord.
Bisect the diameter of an arc opposite to the chord, bisect the chord vertically, and bisect another arc opposite to the chord.
Tangent theorem of circle
The radius perpendicular to the tangent point; The straight line passing through the outer end of the radius and perpendicular to the radius is the tangent of the circle.
Judgment method of tangent: the straight line passing through the outer end of radius and perpendicular to this radius is the tangent of the circle.
Properties of tangent:
(1) The straight line passing through the tangent point and perpendicular to the radius of the tangent point is the tangent of the circle.
(2) The straight line perpendicular to the tangent point must pass through the center of the circle.
(3) The tangent of the circle is perpendicular to the radius passing through the tangent point.