c=πd

Circumference =π×2× radius c=2πr

1. A point set whose distance to a fixed point is equal to a fixed length is called a circle. This fixed point is called the center of the circle and is usually represented by the letter "O".

2. The straight line connecting the center of the circle and any point on the circumference is called radius, which is usually represented by the letter "R".

3. The line segment with two ends on the circumference passing through the center of the circle is called the diameter, which is usually represented by the letter "D".

The radius of extended data perpendicular to the tangent point; The straight line passing through one 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.

Reference circumference _ Baidu Encyclopedia