66
Length of a broken line, perimeter of a polygon
Textbook: Part 2, lesson 63, pp. 48–49
GoalLength of a broken line; perimeter of a polygon.
New words
broken line · siniq chiziqsegment (link) of a broken line · bo‘g‘inpolygon · ko‘pburchakside · tomon
Explanation
A broken line is made of several segments (links). The length of a broken line is the sum of the lengths of all its links. A closed broken line together with its inside is called a polygon. The sum of the lengths of all sides of a polygon is called its perimeter.
Worked examples
Broken line ABCDE has links 3 cm, 4 cm, 2 cm, 5 cm: its length is 3 + 4 + 2 + 5 = 14 cm.
A triangle has sides 34 dm, 39 dm, 32 dm: its perimeter is 34 + 39 + 32 = 105 dm.
Class activity
“Broken line from string”: children shape a string into a broken line (pencils as pins), measure each link with a ruler and find the total length. Close it into a polygon and find the perimeter.
Practice
1
A broken line has links 3 cm, 4 cm, 2 cm, 5 cm. How many cm long is it?
14
2
A triangle has sides 34 dm, 39 dm and 32 dm. What is its perimeter in dm?
105
3
All sides of a pentagon are 5 cm. What is its perimeter in cm?
25
4
A running track is 900 m long. Parts of 320 m and 250 m are known. How many m is the unknown part?
330