The unpopular theorem of mathematical round

Theorems about circles are:

1, tangent theorem

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.

2. Tangent length theorem

Length of two tangents from a point outside the circle to the circle, etc. , the line between this point and the center of the circle bisects the included angle of the tangent.

3. Cutting line theorem

The tangent and secant of the circle intersect at point P, the tangent intersects at point C, and the secant intersects at points A and B, so PC 2 = PA Pb.

Let ABP be the secant of ⊙O, PT be the tangent of ⊙O, and the tangent point is T, then PT? =PA PB

4. Secant theorem

The product of two secant lines drawing a circle from a point outside the circle to the distance between each secant line and the intersection of the circle is equal.

A straight line and an arc have two common points, so we say that this straight line is the secant of this curve.

5, hanging string theorem

The diameter perpendicular to the chord bisects the chord and the two arcs it faces.

6. Chord Angle Theorem

The tangential angle is equal to the corresponding circumferential angle. (Chord tangent angle is the angle between tangent and chord. )

Representation of a circle:

1, circle-⊙;

2. Radius —r or r (letter indicated by the radius of the outer ring in the ring);

3, the center of the circle-O;

4, arc-⌒;

5. diameter -d? ;

6. fan arc length -l? ;