Perimeter and Area of Plane Shapes
Perimeter is the distance round the edges of a shape/object.
Perimeter of rectangle
1.
Find the perimeter of the rectangle below
(a)
A
B
10 cm
5 cm
5 cm
D
C
10 cm
Perimeter = (AB + BC +CD + AD) cm
P = (10 + 5 +10 + 5) cm = 30 cm
(b)
A
B
13 cm
7 cm
D
C
Perimeter = 2(L + b) cm
P= 2(13 + 7) cm
P = 2(20) cm
P = 40 cm
OR
Since opposite side of a square is equal
A
13 cm
7 cm
D
B
7 cm
13 cm
Perimeter = (AB + BC +CD + AD) cm
P = (13 + 7 +13 + 7) cm = 40 cm
C
Classwork
Find the perimeter of the rectangle below:
1. L = 8 cm , b = 4 cm
2. L = 9 cm , b = 6 cm
3. L = 12 cm , b = 9 cm
Page 173 Ex 23.2
Perimeter of Square
2.
Find the perimeter of the square below
A
B
L =3cm
C
D
Perimeter = 4L
P = 4 x 3 = 12cm
OR
Recall: Since all the sides of a square are equal
A
3cm
B
3cm
3cm
D
3cm
C
Perimeter = (AB + BC +CD + AD) cm
P = (3 + 3 + 3 + 3) cm = 12 cm
Classwork
Find the perimeter of the square below:
1. L = 4 cm
2. L = 6 cm
3. L = 9 cm
Area of Plane Shapes
Area is the amount of surface space enclosed by a perimeter. That is, the space
inside the shape.
Area of Rectangle
Examples:
1. Find the Area of the rectangle below:
A
B
B=5cm
D
L
=
C
7cm
Area = L x B
A = 7cm x 5cm
A = 35 cm2
Classwork
Find the Area of the rectangle below:
1. L = 8 cm , b = 4 cm
2. L = 9 cm , b = 6 cm
3. L = 12 cm , b = 7 cm
Area of Square
2. Find the area of a square below:
A
B
L=5cm
D
C
Area = L x L
A = 5cm x 5cm = 25cm2
Classwork
Find the Area of the square below:
1. L = 4 cm
2. L = 6 cm
3. L = 7 cm