Page 180 - Start Up Mathematics_4

Perimeter of curved shapes

To find the perimeter of any curved object, stretch a thread along its boundary. Then open
it and measure the length using a ruler (or scale).

Example 4: Find the perimeter of a circle of radius 2 cm.

Solution: Draw a circle of radius 2 cm. Take a thread and stretch it along
the boundary of the circle to complete one round. Open the 2 cm
thread and measure it using a ruler (or scale). The length of
the thread is the perimeter (or circumference) of the circle.

mm 1 cm 2 3 4 5 6 7 8 9 10 11 12 13 14 15

6
5
Perimeter using a square grid 4 3 2 1 1/16''
A B
We can find the perimeter of any plane figure by drawing it on a
squared sheet of paper. D C
E F
Example 5: Find the perimeter of the given figure. Each side of
the square in the grid is of 1 cm. H G

Solution: Perimeter of ABCDEFGH = AB + BC + CD + DE + EF + FG + GH + HA
= 3 cm + 1 cm + 1 cm + 1 cm + 2 cm +
1 cm + 4 cm + 3 cm

= 16 cm

EXERCISE 13.4

1. Find the perimeter of the following shapes.
6 cm 2 cm 2 cm
(a) (b) (c)
4 cm 4 cm
4 cm 4 cm
2 cm
2 cm
6 cm 3 cm

2 cm 2 cm 2 cm 2 cm 4 cm
(d) (e) (f) 2 cm 2 cm
4 cm 4 cm 3 cm 3 cm

4 cm 4 cm
6 cm
5 cm
1 cm

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