11
Review: area and perimeter
Textbook: Part 1, lesson 11, pp. 34–36
GoalReview the perimeter and area of rectangles, squares and regular polygons.
New words
perimeter · perimetrarea · yuzregular polygon · muntazam ko‘pburchakside · tomon
Explanation
The perimeter of a polygon is the sum of the lengths of all its sides. Rectangle: P = (a + b) × 2, S = a × b. Square: P = a × 4, S = a × a. A regular polygon has all sides equal, so with n sides P = a × n. Area is measured in square units (cm², m²).
Worked examples
A rectangle 18 cm by 7 cm: P = (18 + 7) × 2 = 50 cm, S = 18 × 7 = 126 cm².
A regular pentagon with side 14 dm: P = 14 × 5 = 70 dm.
Class activity
“Measure it”: groups measure the length and width of the board or a notebook page and calculate its perimeter and area.
Practice
1
A garden is 25 m long and 12 m wide. What is its perimeter in metres?
74
2
What is the area in cm² of a square with side 9 cm?
81
3
What is the perimeter in cm of a regular hexagon with side 8 cm?
48
4
A rectangle has area 360 m² and length 24 m. How many metres wide is it?
15