What is Circle ?

A secant is a line of indefinite length intersecting the circle at two points, the segment of it within the circle being a chord. A tangent to a circle is a straight line touching the circle at only one point, the point of contact, or tangency, and is always perpendicular to the radius drawn to this point.

A circle is a round shaped figure that has no corners or edges.

A circle is a round, two dimensional shape that looks similar to the letter ‘O’.

In strict mathematical language, circle refers to the boundary of the shape while ‘disk’ is used to refer to the whole shape, including the inside.

. A circle is inscribed in a polygon if each side of the polygon is tangent to the circle; a circle is circumscribed about a polygon if all the vertices of the polygon lie on the circumference. The length of the circumference C of a circle is equal to π (see pi) times twice the radius distance r, or C=2πr. The area A bounded by a circle is given by A=πr2. Greek geometry left many unsolved problems about circles, including the problem of squaring the circle, i.e., constructing a square with an area equal to that of a given circle, using only a straight edge and compass; it was finally proved impossible in the late 19th cent. (see geometric problems of antiquity). In modern mathematics the circle is the basis for such theories as inversive geometry and certain non-Euclidean geometries.

A straight line from the center of a circle to the edge is called the radius.

The circle figures significantly in many cultures. In religion and art it frequently symbolizes heaven, eternity, or the universe.

The center of a circle is the center point in a circle, from which all the distances to the points on the circle are equal.
Here, point P is the center of the circle.

A straight line that passes from one side of a circle to the other through the center is called the diameter.

The distance around the outside of a circle is called the circumference.

The center of a circle is the center point in a circle, from which all the distances to the points on the circle are equal.
Here, point P is the center of the circle.

The diameter (meaning "all the way across") of a circle is a straight line that goes from one side to the opposite and right through the centre of the circle. Mathematicians use the letter d for the length of this line.

All points on the edge of a circle are the same distance to the center.

The value of Pi (π ) to 2 decimal places is 3.14, it comes in handy when working out the circumference and area of a circle.

The circumference (meaning "all the way around") of a circle is the line that goes around the centre of the circle. Mathematicians use the letter C for the length of this line.

The circumference of a circle can be found with the following formula: Circumference = π d

π can be measured by drawing a large circle, then measuring its diameter (d) and circumference (C). This is because the circumference of a circle is always π times its diameter.

The area of a circle can be found with the following formula: Area = π r²

π can also be calculated by only using mathematical methods. Most methods used for calculating the value of π have desirable mathematical properties. However, they are hard to understand without knowing trigonometry and calculus. However, some methods are quite simple, such as this form of the Gregory-Leibniz series:

An arc is part of the circumference of a circle.

A chord is a straight line joining two points on a circle, the diameter is an example of a chord (the longest possible one).

A segment is the region between a chord and the arc it joins.

A tangent is a straight line that touches a single point of a circle.

A sector is the region between an arc and two radii.

The full arc of a circle measures 360 degrees.