The diameter of a circle is a line which cuts directly through the middle of the circle.
The radius is a line connecting the outer part of the circle to the center. It is half the diameter.
When a triangle is formed in a circle with two sides being radii, the two sides are equal.
Chord
A line that links two points on a circle or curve.
The midpoint of the chord passes through the center of the circle.
Double Chord
The two mid points cross in the center of the circle.
When the diameter passes through a chord, a 90° forms. It also identifies the midpoint of the chord.
* If a line bisects a chord and is perpendicular to it, then it passes through the centre of the circle.
* If a line bisects a chord and passes through the centre, then the two lines are perpendicular.
* If a line passes through a chord and the center of a circle, the point of intersection is the middle of the chord.
Tangents
A tangent is a line that intersects a circle at exactly one point.
It is created by taking the two points of a secant line and making them closer together.
Central and Inscribed Angles
The vertex of an inscribed angle is always on the edge of the circle.
Central
Inscribed
* Central angles containing equal arcs / the same arc are similar.
* Inscribed angles containing equal chords / the same chord are similar.
* Inscribed angles containing equal / the same arcs are similar.
If a central angle and an inscribed angle both contain the same chord or arc, the central angle is always doubled the inscribed angle. Therefore, the inscribed angle is always half of the central angle.
