circle

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Perfectly round shape, the path of a point that moves so as to keep a constant distance from a fixed point (the centre). A circle has a radius (the distance from any point on the circle to the centre), a circumference (the boundary of the circle, part of which is called an arc), diameters (straight lines crossing the circle through the centre), chords (lines joining two points on the circumference), tangents (lines that touch the circumference at one point only), sectors (regions inside the circle between two radii), and segments (regions between a chord and the circumference).

The ratio of the distance all around the circle (the circumference) to the diameter is an irrational number called π (pi), roughly equal to 3.1416.

A circle of radius r and diameter d has a circumference C = πd, or C = 2πr, and an area A = πr². The area of a circle can be shown by dividing it into very thin sectors and reassembling them to make an approximate rectangle. The proof of A = πr² can be done only by using integral calculus.

Angles within a circle can be calculated using the circle theorems.

Red and white are the national colours, derived from a 13th-century emblem bearing a white eagle on a red field. Effective date: 23 March 1956. >>