84
Sides of rectangles and squares
Textbook: Part 3, lesson 79, pp. 16–17
GoalKnow that opposite sides of a rectangle and a square are equal; find the perimeter.
New words
opposite sides · qarama-qarshi tomonlarlength · bo‘yiwidth · eniperimeter · perimetr
Explanation
Opposite sides of a rectangle and of a square are equal: AB = CD and BC = AD. In a square all four sides are equal. The perimeter is the sum of all sides. A rectangle 8 cm long and 4 cm wide has perimeter 8 + 4 + 8 + 4 = 24 cm.
Worked examples
In rectangle ABCD, if AB = 8 cm then CD is also 8 cm.
A yard 40 m long and 25 m wide needs 40 + 25 + 40 + 25 = 130 m of fence.
Class activity
“Opposite pairs”: children cut out a rectangle, measure its sides and mark sides of equal length in the same colour.
Practice
1
In rectangle ABCD, AB = 7 cm. How many cm is CD?
7
2
A yard is 40 m long and 25 m wide. How many metres of fence are needed to go around it?
130
3
A rectangle with sides 9 cm and 5 cm has a perimeter greater than that of a square with side 5 cm. By how many cm?
8
4
Calculate in a convenient way: (52 + 49) − 39 = ?
62
5
On day one 240 bricks were delivered, on day two 130 more than that. In three days 800 bricks came in total. How many came on day three?
190