Page 195 - ICSE Math 6

18 Circles

Key Concepts

• Circle—Centre, Radius, Diameter, Arc, Sector, Chord, Segment, Semicircle, Circumference, Interior and Exterior
• Construction of Circles

Circle

A circle is a simple closed curve formed by all the points in a plane which are Circular
at a fixed distance from a fixed point in the plane. This fixed point lies inside region
the circle. The area enclosed by a circle is known as the circular region. O
In the adjoining figure, a circle is shown. The point O is the fixed point from Fixed
which all the points on the circle are at a fixed distance. The shaded region point
is the circular region.

Parts of a circle
Centre

The fixed point inside the circle from which all the points on the circle are at
a fixed distance is known as the centre of the circle. In the adjoining figure, O
O is the centre of the circle.

Radius

The distance between the centre and any point on the circle is known as the
radius of the circle. It is the fixed distance which is used to define a circle. In O A
the adjoining figure, line segment OA is a radius of the circle.

Chord
Q
A chord of a circle is a line segment joining any two points on the circle. It P
lies inside the circle. In the adjoining figure, line segment PQ is a chord of O
the circle.

Segment
Maths Info
A chord divides a circle into two parts and each part is known as a
segment. The part greater than half of the circular region is known Quarter of a circle is known as
as the major segment and the other part which is less than half of quadrant and it is bounded by two
mutually perpendicular radii.
the circular region is known as the minor segment.
Minor segment
Points to remember Q
• Major segment contains the centre of the circle. P O

• Diameter divides a circle into two equal segments. Major segment

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