Diameter

Straight line segment that passes through the centre of a circle Circle with Circumference C Diameter D Radius R Centre or origin O In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for the diameter of a sphere. In more modern usage, the length d of a diameter is also called the diameter. In this sense one speaks of the diameter rather than a diameter (which refers to the line segment itself), because all diameters of a circle or sphere have the same length, this being twice the radius r: d = 2 r ; r = 1 2 d . {\displaystyle d=2r;\qquad r={\tfrac {1}{2}}d.} The word "diameter" is derived from Ancient Greek διάμετρος (diametros) 'diameter of a circle', from διά (dia) 'across, through' and μέτρον (metron) 'measure'. It is often abbreviated DIA, dia, d, or ∅ . {\displaystyle \varnothing .} Constructions With straightedge and compass, a diameter of a given circle can be constructed as the perpendicular bisector of an arbitrary chord. Drawing two diameters in this way can be used