# circles

### come and learn about circles with us

## DEFINITION:

**circle**is a simple closed shape. It is the set of all points in a plane that are at a given distance from a given point, called the center . The distance between any of the points and the center is called the radius.

Parts Of The Circle:

- Center: the point equidistant from the points on the circle.
- Chord: a line segment whose endpoints lie on the circle.
- Diameter: a line segment whose endpoints lie on the circle and which passes through the center It is a special case of a chord, namely the longest chord, and it is twice the radius.
- Radius: a line segment joining the center of the circle to any point on the circle itself. it is half a diameter.

## history of circles:

The word *circle* derives from the Greek κίρκος/κύκλος (*kirkos/kuklos*),meaning "hoop" or "ring".The origins of the words *circus* and *circuit* are closely related.

The circle has been known since before the beginning of recorded history. Natural circles would have been observed, such as the Moon, Sun, and a short plant stalk blowing in the wind on sand, which forms a circle shape in the sand. The circle is the basis for the wheel, which, with related inventions such as gears, makes much of modern machinery possible. In mathematics, the study of the circle has helped inspire the development of geometry, astronomy, and calculus.

Early science, particularly geometry and astrology and astronomy, was connected to the divine for most medieval scholars, and many believed that there was something intrinsically "divine" or "perfect" that could be found in circles.

Some highlights in the history of the circle are:

- The Rhind papyrus gives a method to find the area of a circular field.

- In Plato's Seventh Letter there is a detailed definition and explanation of the circle. Plato explains the perfect circle, and how it is different from any drawing, words, definition or explanation.

## types of circles

- secant circles
- interior circles
- exterior circles
- internally tangent
- externally tangent

## perimeter and area of a circle

the area of a circle is =πR*R