# Area and Circumference of Circle

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A circle is the locus of all the points in a plane which are at a constant distance from a fixed point. The fixed point is called the centre of the circle and the constant distance is called the radius of the circle. A chord of a circle passing through its centre is called its diameter. Diameter is the longest chord of the circle. The diameter of a circle is twice its radius. A circle with its centre at origin and radius 1 unit is called a unit circle.

The length of the boundary of a circle is called its circumference. It is also called the perimeter of the circle. Pi is the ratio of the circumference of a circle to its diameter.

It is denoted by the symbol ‘p’. Pi is an irrational number as it is non-repeating and non-terminating. Value of up to first 100 decimal places: 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679

In calculations, value of pi is taken as 3.14 or 22/7.

Circumference of a circle = p?× d, where d is the diameter of the circle.

If r is the radius of a circle, then its circumference = 2 pr

The region enclosed by the circumference of the circle is called its area.

Area of a circle = p r2 , where r is the radius of the circle.

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