A segment that connects any two points of a circle is called a chord.Passing through the center of a circle, the chord is called its diameter. The diameter denoted by the symbol  or Latin letter D. Diameter (D) twice as long as the radius of curvature (R) and is the greatest possible distance between the points on the circle.Example. The radius of the circle is 20 cm D(diameter)? Then, if R = 20 cm and we know that the length of the diameter equal to the length of the two radii D = 2R = 2*20 = 40 cm
There is a second way to find the diameter of a circle. In this case, we should be known for its length. Mark the circumference of the Latin letter C. Example. C = 60 cm D - ? Solution. From geometry we know that the circumference is given by: C = 2R, where: R is the radius of the circle, and  is an irrational number "PI" equal approximately to 3.14. Then, this formula implies the other: D = With : 3,14. So, D = 60 : 3,14 = 19,12 see