Page 3 - 7-Math-12 CIRCUMFERENCE, AREA AND VOLUME

112.. QCiurcaudmrfearteincceE,qAureaataiondnVsolume eLearn.Punjab

Here, we can also calculate the ratio between circumference eLearn.Punjab
and diameter of the circles given above by finding version: 1.1

the value c where “c” is the circumference and “d” is the diameter
d

of the circles A, B and C as given in the following table.

Circles Circumference Diameter Ratio
(c) (d) (c/d)

A 7.6 2.4 3.1666

B 12.57 4 3.1425

C 19.48 6.2 3.1419

We can see that the ratio between circumference and diameter

is approximately the same. We denote this constant value by a

Greek symbol p the value of which is taken approximately equal to

22 or 3.14.
7

So, we can write the above statement as, circumference (c) = p
diameter (d )

Or simply we can write it as, c = p
d
Therefore, c = dp

But we know that d = 2r

So, c = 2pr

Hence, c = dp or 2pr where ‘c’ is the circumference, ‘d’ is the diameter

and ‘r’ is the radius.

12.1.2 Finding the Circumference of a Circle Using
Formula

Example 1: Find the circumference of a circle with diameter
3.2cm.
Solution:

Diameter (d) = 3.2cm Circumference (c) = ?

Using the formula, c = dp

c = 3.2 × 22 = 10.06cm (up to two decimal places)
7

3