Let us take a circle
Distance around the circle is called circumference of circle.
So, Perimeter of circle is actually circumference of circle.
For a circle with radius r,
Circumference = 2𝜋r
Here,
r is the radius,
and
𝜋 = pi
It’s value is
𝜋 = 3.14159265359……
We write it as
𝜋 = 3.14 or 𝜋 = 22/7
Let’s take some examples
Find circumference of circle with radius 3.5 cm
Radius = r
= 3.5 cm
Circumference = 2𝜋r
= 2 × 22/7 × 3.5
= 2 × 22/7 × 35/10
= 2 × 22/1 × 5/10
= 22 × 5/5
= 22 × 1 = 22 cm
Find circumference of circle with radius 7.0 cm
Radius = r
= 7 cm
Circumference = 2𝜋r
= 2 × 22/7 × 7
= 2 × 22/1 × 1
= 44 cm
Find circumference of circle with diameter 21 cm
Diameter = 21 cm
Radius = r = Diameter/2
= 21/2
Circumference = 2𝜋r
= 2 × 22/7 × 21/2
= 22/7 × 21/1
= 22 × 3
= 66 cm
Find circumference of circle with diameter 42 cm
Diameter = 42 cm
Radius = r = Diameter/2
= 42/2
= 21 cm
Circumference = 2𝜋r
= 2 × 22/7 × 21
= 2 × 22/1 × 3
= 44 × 3
= 132 cm
Find circumference of circle with radius 5 cm
Radius = r
= 5 cm
Circumference = 2𝜋r
= 2 × 3.14 × 5
= 3.14 × 5 × 2
= 3.14 × 10
= 31.4 cm
Find circumference of circle with diameter 30 cm
Diameter = 30 cm
Radius = r = Diameter/2
= 30/2
= 15 cm
Circumference = 2𝜋r
= 2 × 3.14 × 15
= 3.14 × 2 × 15
= 314/100 × 30
= 314/10 × 3
= 942/10
= 94.2 cm
