82
Angles of rectangles and squares
Textbook: Part 3, lesson 77, pp. 12–13
GoalKnow that all angles of a rectangle and a square are right angles and equal.
New words
equal angles · teng burchaklarto fit exactly on top · ustma-ust tushishto fold · buklashto check · tekshirish
Explanation
To see whether two angles are equal, we place one on top of the other. If the vertex fits on the vertex and the sides fit on the sides, the angles are equal. If we fold a cut-out rectangle, its corners fit on top of each other. All angles of a rectangle and a square are right angles and are equal. We can check with a set square.
Worked examples
If we fold a 14 cm by 6 cm rectangle in half, its corners fit on top of each other.
A book 15 cm wide and 23 cm long has four right angles and perimeter 15 + 23 + 15 + 23 = 76 cm.
Class activity
“Fold and check”: children cut a rectangle from paper, fold the corners onto each other and check them with a set square.
Practice
1
How many angles of a rectangle are right angles?
4
2
Are the angles of a square equal to each other?
Yes
3
A book is 15 cm wide and its length is 8 cm more than its width. How many cm long is it?
23
4
Calculate: 540 − (260 − 175) + 120 = ?
575