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\ 19-Nov-2025 Bharat Arora Proof-9 Reader’s Sign _______________________ Date __________

• Diameter: The diameter of a circle is a line segment that passes through the
centre of the circle and has its endpoints on the circle. Here, AB is a diameter of
the circle.

• Circumference: The distance around a circle is called its circumference.
• Chord: A line segment whose endpoints lie on the circle is called a chord of the
circle. Here, PQ is a chord. The diameter is the longest chord of a circle.

• Semicircle: The diameter divides a circle into two equal halves. Each half is
called a semicircle.

• Interior of the circle: The area enclosed by the circumference is called the
interior of the circle. Here, point O lies on the interior of the circle.
• exterior of the circle: The area outside the circumference of the circle is called

the exterior of the circle.
relation between radius and Diameter: The diameter of a circle is twice its

radius, and the radius is half of the diameter.
Diameter = 2 × Radius
B
Diameter
Radius =
2 A
6 cm
example 1. Find the diameter of a circle whose radius is 6 cm. O
Solution. Diameter = 2 × Radius

Therefore, Diameter = 2 × 6 cm = 12 cm.
example 2. Find the radius of a circle whose diameter is 8 cm. C

Diameter
Solution. Radius =
2
8 cm
8 P Q
Therefore, Radius = cm = 4 cm. O
2

Drawing a Circle using a Compass R

Let us draw a circle of radius 3 cm.

Step 1. Fix a sharp pencil firmly in the pencil-

holding arm of the compass.

Step 2. Place the metal tip of the compass at the

0 mark on the ruler and open it so that the W X Y Z [ \ ] ^ _
W cm X Y Z
pencil tip aligns with the 3 cm mark.

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Geometry