### Mathematics Class VII

Integers
Fractions and Decimals
Exponents and Powers
Algebraic Equations
Simple Linear Equations
Lines and Angles
Comparing Quantities
Congruence of Triangles
Rational Numbers
Perimeter and Area
Data Handling
Practical Geometry
Symmetry
Visualising Solid Shapes

# Circles

It is a round, closed shape.

The circumference of a Circle

The circumference of a circle refers to the distance around the circle.

• Radius: A straight line from the Circumference till the centre of the circle.
• Diameter: It refers to the line from one point of the Circumference to the other point of the Circumference.
• π (pi): It refers to the ratio of a circle’s circumference to its diameter.

Circumference(c) = π × diameter

C = πd

= π × 2r

diameter (d) = twice the radius (r)

d = 2r

Example

What is the circumference of a circle of diameter 12 cm (Take π = 3.14)?

Solution

C = πd

C = 3.14 × 12

= 37.68 cm

##### Area of Circle

Area of the circle = πr2

Example

Find the area of a circle of radius 23 cm (use π = 3.14).

Solution

R = 23 cm

π = 3.14

Area of circle = 3.14 × 232

= 1,661 cm2

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