9
Review: rectangles
Textbook: Part 1, lesson 9, pp. 28–30
GoalReview finding the perimeter and area of rectangles and squares.
New words
perimeter · perimetrarea · yuzlength and width · bo‘yi va enisquare centimetre · kvadrat santimetr
Explanation
The perimeter is the sum of the lengths of all sides. For a rectangle P = (a + b) × 2, for a square P = a × 4. The area of a rectangle is S = a × b, of a square S = a × a. Area is measured in square units: 1 dm² = 100 cm², 1 m² = 100 dm².
Worked examples
An 8 cm by 5 cm rectangle: P = (8 + 5) × 2 = 26 cm, S = 8 × 5 = 40 cm².
A square with side 6 dm: P = 6 × 4 = 24 dm, S = 6 × 6 = 36 dm².
Class activity
“Shape on squared paper”: children draw a rectangle 6 squares long and 3 wide, count squares for the area and sides for the perimeter, then check with the formulas.
Practice
1
A rectangle is 12 cm long and 5 cm wide. What is its perimeter in cm?
34
2
What is the area of the same rectangle in cm²?
60
3
A square has side 9 dm. What is its perimeter in dm?
36
4
A field is 60 m long and its width is 3 times smaller than its length. What is the perimeter in metres?
160
5
How many square centimetres is 2 dm²?
200