Page 188 - Math Genius C4

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Perimeter

Ankit jogs every morning. He wants to jog around the

park. So, he starts jogging from a tree, and when he
returns to the tree he has jogged the entire path around

the park.
The length of the entire path shown by
the black line is the perimeter of the park Knowledge Desk

around which Ankit jogs. Thus, the length of The word perimeter is derived from the
the boundary of a closed figure is called its Greek word “Perimetros”. “Peri” means

perimeter. “around” and “Metros” means “measure”.
Perimeter of a Polygon

We know that a polygon is a closed figure formed by line segments.
The perimeter of a polygon is the sum of the length of its sides (line segments)

enclosing the figure.

Perimeter of a polygon = Sum of the lengths of its sides

example 1: Find the perimeter of the following closed figure.

(a) 8 m (b) 3 m

5 m 2 m
7 m
5 m 8 m 10 m 2 m
5 m

10 m 15 m

Solution: (a) Perimeter of the given figure
Be Aware
= Sum of the lengths of its sides We always write the

= 5 m + 8 m + 7 m + 10 m = 30 m unit of measurement
after the result.
(b) Perimeter of the given figure

= Sum of the lengths of its sides
= 8 m + 3 m + 5 m + 10 m + 2 m + 2 m + 5 m + 15 m

= 50 m

The perimeter of a polygon can also be found using square grid paper.
If the sides of a polygon lie on the grids of a square paper, we count the number

of unit lengths along the boundary of the figure. The total number of unit lengths
counted is the perimeter of the figure.

186 Mathematics-4