Plane Shapes 2: Perimeter – Perimeter of a Rectangle and Square
Perimeter is the outside boundary or edges of a plane shape.
Example
- Irregular shapes. Measure the perimeter of the quadrilateral ABCD in the diagram below.
Solution
AB = 22mm = 2.2cm
BC= 27mm = 2.7cm
CD= 10mm =1.0cm
DA= 35mm = 3.5cm
Total 94mm = 9.4cm
- Regular shapes: Find in cm, the perimeter of the regular hexagon ABCDEF below.
Solution
Length AB= 1.6cm ,
there are 6 equal sides
Perimeter = 6 x 1.6cm
= 9.6cm
Using Formulae to Calculate Perimeters.
Examples
- A rectangular piece of land measures 57m by 42m. What is the perimeter of the land.
Solution
Perimeter of land = 2(L + B)
= 2(57 +42) m
= 2(99) m = 198m.
To calculate Length = perimeter of rectangle – breadth
2
To calculate Breadth = perimeter of rectangle/2 – length
- A rectangle has a perimeter of 74m. Find
- a) the length of the rectangle if its breadth is 17.
- b) the breadth of the rectangle if its length is 25m.
Solution
a) Length = perimeter of rectangle/2 – breadth , 74m/2 -17m = 37m – 17m = 20m
b) Breadth= perimeter of rectangle/2 – length, 74m/2 – 25m = 37m – 25m = 12m
Squares
A square is a regular four sided shape.
If the length of one side of a square is L.
Perimeter of square = L x 4 = 4L
Length of side of square = perimeter of square/4
Example
- Calculate the perimeter of a square of side 12.3cm.
Solution
Perimeter of square = 4L, 12.3 x 4 = 49.2cm
- A square assembly area has a perimeter of 56m. Find the length of the side of the assembly area.
Solution
Length of square = perimeter/ 4 , 56m/4 = 14m
Assignment
- A rectangular field measure 400m by 550m. What is the perimeter of the field.
- Calculate the perimeter of a square of side 15cm.
- A length of wire is bent to make a square of side 3.2cm. a) what is the length of the wire in the square. b)if the wire is silver, costing ₦50 per centimeter, what is the cost of the square.