Third Term Lesson Note for Week Four
Class : JSS One
Subject : Mathematics
Topic : Perimeter and Area of plane shapes.
Duration : 80 Minutes
Period : Double Period
Reference Book :
- Essential Mathematics for Junior Secondary School, JSS 1.
- New General Mathematics for Junior Secondary School, JSS 1.
- Lagos State Unified schemes of work for Junior Secondary School, JSS 1 – 3.
- Online Resources
Instructional Material : Chart showing basic tips in relating word problems to form simple equation.
Key Vocabulary : plane Shapes , perimeter, area, triangle, rectangle, parallelogram, square, circle, etc.
Previous Knowledge : Learners are familiar with geometry of plane shapes and the properties.
Learning Objectives : By the end of the lesson learners will be able to :
i. Define Perimeter and Area
ii. State the formula for finding perimeter of plane shapes and solve examples
iii. Identify and state formula for finding area of plane shapes with several worked examples
Content :
AREA AND PERIMETER OF PLANE SHAPES
Perimeter : The perimeter of a plane shape is the length of its outside boundary. This means the distance round its edges.
Examples :
1. The length of a rectangular room is 5m and the width is 4m. Find the perimeter of the room.
Solution :
The length of the room = 5m
The width of the room = 4m
Perimeter = 2(L + w)
Perimeter = 2(5 + 4)m
= 2(9)m
= 2 x 9m
= 18m
2. The perimeter of a square is 2580cm. find the length of the square in meter.
Solution :
P = 2580cm = 25.8m
P = 4 x length = 4L
L = 25.8m ÷ 4
L = 6.45m
Therefore, the length of the square = 6.45m
3. Calculate the perimeter of a triangle with dimensions 4.2m, 3.6m and 5.7m.
Solution :
Perimeter = (4.2 + 3.6 + 5.7) m
Perimeter = 13.5m
4. A parallelogram has sides measuring 200mm by 150mm. what would be the length of the side of a square having the same perimeter?
Solution :
Length of parallelogram = 200mm
The width of the parallelogram = 150mm
Perimeter = 2( L + w)
Perimeter = 2(200 + 150) mm
Perimeter = 2 x 350 = 700mm
But
Perimeter of the square = 4 x length = 4L
4L = 700mm
Divide both sides by the coefficient of l
L = 700mm ÷ 4
= 175mm
Therefore, the length of the square = 175mm
4. Calculate the perimeter of a circle of diameter 14cm.
Note :
1. The perimeter of a circle is called circumference and
2. The diameter (D) is twice the radius (r), thus D = 2r
Solution :
Method 1: circumference = πd
C = 22/7 x 14
C = 44cm
Method 2 :
R = D/2
= 14 ÷ 2
= 7cm
C = 2πr
C = 2 x 22/7 x 7
C = 44cm
AREA : Area of shapes is the measure of amount of surface it covers or occupies.
Examples :
1. Calculate the area of rectangular room with dimension 250cm by 200cm.
Solution :
A = (250 x 200) square cm
A = 50 000 cm square or 50000 cm²
2. Find the area of a square of sides 14cm.
Solution :
A = 14 cm x 14 cm
A = 196 cm²
3. Evaluate the area of a parallelogram with base 8cm and height 9cm.
Solution :
A = 8 cm x 9 cm
A = 72 cm square or 72 cm²
4. Calculate the area of a trapezium with parallel sides 10cm and 18cm and height 12cm.
Solution :
Area = ½ (a + b) h
Area = ½ (10 + 18)cm x 12cm
= ½ (28)cm x 12cm
= 14cm x 12cm
Area = 168 cm square or 168 cm²
Evaluation :
Do these
Exercise 18.2 pg 198 No (2, 3,4 & 5)
Exercise 18.3 pg 200 No (2, 3, 4 & 5)
Assignment :
Exercise 18.6 pg 209 No (2, 4, 5,9 & 10)