Circle and its part

Actually the circle is the one kind of line means the type of line and also the set of points which are equidistant to any fix point of plane. This constant distance called the Radius of circle and that fix point are called the Center of circle.

The radius of a circle is the length of the line from the center to any point circle on its edge. The radius of circle is always constant. The plural form of the radius is - radii (pronounced "ray-dee-eye"). Sometimes the word 'radius' is used to refer to the line itself. In that sense you may see "draw a radius of the circle". In the more recent sense, it is the length of the line, and so is referred to as "the radius of the circle is 2 centimeters"

(1) DIAMETER

               when D = diameter of the circle

Radius is simply half the diameter.

(2) CIRCUMFERENCE

 

when C = circumference of the circle

         D = diameter of the circle

The ratio of a circle's circumference to its diameter is π (pi), an irrational constant approximately equal to 3.141592654. Thus the length of the circumference C is related to the radius r and diameter d.

(3) AREA ENCLOSED

             when A = the area of the circle

As proved by Archimedes, the area enclosed by a circle is equal to that of a triangle whose base has the length of the circle's circumference and whose height equals the circle's radius,which comes to π multiplied by the radius squared:

Equivalently, denoting diameter by d,

that is, approximately 79 percent of the circumscribing square (whose side is of length d).

The circle is the plane curve enclosing the maximum area for a given arc length. This relates the circle to a problem in the calculus of variations, namely the isoperimetric inequality.

The history of Circle

The word "circle" derives from the Greek, kirkos "a circle," from the base ker- which means to turn or bend. 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 civilisation 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.