83
Drawing a right angle
Textbook: Part 3, lesson 78, pp. 14–15
GoalDraw a right angle with a set square; recognise a right triangle.
New words
set square · goniyaright triangle · to‘g‘ri burchakli uchburchakto construct, to draw · yasashperimeter · perimetr
Explanation
To draw a right angle, put the right-angle corner of a set square on a point and draw lines along its two sides. A triangle with one right angle is a right triangle. Its perimeter is the sum of its three sides. Draw two sides, then measure the third with a ruler.
Worked examples
In a right triangle with sides 3 cm and 4 cm, the third side is 5 cm: perimeter 3 + 4 + 5 = 12 cm.
If we fold a square sheet twice, a right angle appears at the fold.
Class activity
“Set-square masters”: children mark a point, draw a right angle with a set square, turn it into a right triangle and measure its sides.
Practice
1
What is a triangle with one right angle called?
A right triangle
2
A right triangle has sides 3 cm, 4 cm and 5 cm. What is its perimeter in cm?
12
3
A right triangle has two sides 6 cm and 8 cm, and the measured third side is 10 cm. What is its perimeter in cm?
24
4
Calculate: (412 + 235) − 158 = ?
489
5
Children assembled 14 fish, 17 bird and 12 butterfly shapes. How many shapes in total?
43