Diameter, chords, and secants

In a circle, the diameter is a special chord that passes through the center and has the maximum possible length. Any segment joining two points on the circle is a chord. A secant is a line (not just a segment) that intersects the circle at exactly two points.

Important properties

• The diameter is twice the radius: $d = 2r$.

• All diameters of a circle have the same length.

• The diameter divides the circle into two equal halves.

• A chord that passes through the center is a diameter.

• The perpendicular from the center of the circle to a chord bisects the chord.

• A secant contains a chord as the part inside the circle, but extends beyond the circle.