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Concept of Circles

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  • The collection of all the points in a plane, which are at a fixed distance from a fixed point in the plane, is called a circle.

  • The fixed point is called the centre of the circle.

  • The fixed distance is called the radius of the circle.
    The line segment joining the centre and any point on the circle is also called a radius of the circle. That is, ‘radius’ is used in two senses in the sense of a line segment and also in the sense of its length.

  • The Perimeter of the circle is called the circumference.

  • The line segment, joining any two points on the circumference of the circle, is called a chord.

  • A chord, which passes through the centre of the circle is called the diameter, and is the largest chord of the circle which is equal to two times the radius.


  •  A sector is a region in the interior of a circle enclosed by an arc on one side and a pair of radii on the other two sides.
  • A segment of a circle is a region in the interior of the circle enclosed by an arc and a chord.

  • A diameter of a circle divides it into two equal parts; each part is a semi-circle. A semi-circle is half of a circle, with the endpoints of diameter as part of the boundary. | Circles

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