FINDING THE AREA OF A CIRCLE

STAGE ONE THE RADIUS AND THE DIAMETER

A B

C

O

The distance from the center of the circle to

many point at its circumference in always

constant.

The distance is called the radius (r)

So we get:

AO = OB = OC this is called the radius, thus

AB = 2OA or AB = 2OB this called the diameter

(d)

From the statement we get the diameter is

twice from the radius or

d = 2r

FINDING THE AREA OF A CIRCLE

STAGE TWO THE VALUE OF π 1. Draw a circle on a piece of paper by using

a compass. Draw the radius as you like.

2. Cut out the picture

3. Measure the circumference of the circle

by using a thread and then cut it.

Circumference is the distance around the

outside of circle.

4. Measure the thread

5. Calculate the diameter (centre line) of the

circle.

6. Calculate the value of

7. Repeat step 1-6 with different radius

d

C

diameter

ncecircumfere

FINDING THE AREA OF A CIRCLE

STAGE TWO THE VALUE OF π

π =

π = 3.14 atau

π =

d

C

diameter

ncecircumfere

7

22

FINDING THE AREA OF A CIRCLE

STAGE THREE AREA OF A CIRCLE 1. Draw a circle on a piece of paper using the

compass. Then draw lines which divide the circle

of the same size as show in the picture on the

leaf.

2. Cut all the inner part of the circle then arrange

them as shown in the following picture

3. The more you divide the circle, the more the

shape will look similar to a rectangular shape

with the length 0.5 circumference of the circle

and the width r.

From the previous activity, we found out that

or C=π.d = 2π.r

Therefore, the area of the circle is = area of retangular

=length x width

=0.5.C.r

=0.5.2πr.r

=π.r.r

r

0.5 circumference of the circle d

C

diameter

ncecircumfere