Page 1 - Lesson Note-1Introduction,Terms related to Circle Ch.- 10 Circle
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SAI International School
Class –IX
Mathematics
Chapter-10: Circles Lesson note-1
Sub topics: Introduction of Circles and its Related Terms.
We come across many objects in daily life, which are round in shape, such as wheels of
a vehicle, bangles, dials of many clocks, coins of denominations Re 1 and Rs 5, key
rings, buttons of shirts, etc. In a clock, you might have observed that the second’s hand
goes round the dial of the clock rapidly and its tip moves in a round path. This path
traced by the tip of the second’s hand is called a circle.
A circle is the locus (Collection) of the points in a plane which are at a fixed
distance from a fixed point.
The fixed point is called centre.
The fixed distance is called radius.
Twice of the radius is called Diameter.
A circle divides the plane on which it lies into three parts.
They are: inside the circle, which is also called the interior of the circle; on the circle
and Outside the circle, which is also called the exterior of the circle.
The circle and its interior make up the circular region.
The perimeter of circle is called circumference.
The area of the circle is the region bounded by it in a plane.
Circles Terminologies
Annulus-The region bounded by two concentric circles. It is basically a ring-shaped
object.
