Area of Shapes

1
Area of Shapes

• The area of a shape is the space it occupies.
• Try guessing the name of these shapes first

Parallelogram
Trapezium
Square
Rectangle
Circle
Triangle
2
The Square

• Area l x b

e.g. Find the area of a square of side 3.5
cm.
Discuss and work out this example together
with your friend.
b
A l x b A 3.5 cm x 3.5 cm 12.25 cm2
l
3
The Rectangle

• Area l x b

e.g. Find the area of a rectangle of
length 3.5 cm and height 80 mm.
Discuss and work out this example together.
Since units must be the same 10 mm 1 cm 80 mm
80 mm 10 8 cm A l x b A 3.5 cm x 8
cm 28 cm2
b
l
4
The Parallellogram

• Area b x h

e.g. Find the area of a parallelogram
correct to 1 d.p.
height
h
base
b
A b x h A 10.3 cm x 3.8 cm 39.14 cm2
39.1 cm2
Discuss and work out this example together.
5
The Triangle

• Area ½ b? h

e.g. Find the area of triangle ABC correct
to the nearest cm2.
height
h
base
b
A ½b x h A ½ x 4 cm x 11.7 cm 23.4 cm2
23 cm2
Discuss and work out this example together.
6
The Trapezium

• Area ½h(a b)

e.g. Find the area of the trapezium.
Length of side a
a
h
height
Length of side b
b
Decide about the values of a, b and h to find
the area.
h 6cm, a 8.5 cm, b 12 cm A ½h(a
b) A ½ x 6 cm x (8.5 cm 12 cm) ½ x 6 cm x
20.5 cm 61.5 cm2
a
b
h
a
b
? Area of trapezium ½ h(a b)
The 2 trapeziums form a parallelogram
Area of parallelogram h(a b)
Area of 1 trapezium is half h(a b)
Copy the trapezium
7
The Circle

• Area p r2

e.g. The diameter of a circle is 19 cm. Find,
correct to nearest whole number, the area of
a circle.
r 19 cm 2 9.5 cm. A p r2 p x 9.5
cm x 9.5 cm 283.5 cm2 284 cm2
Radius
r
Find the radius first and then work out this
example together.
Centre
Remember the radius of a circle is half the
diameter.