Page 206 - Start Up Mathematics_6

We know, area of a square of side 1 cm is 1 sq. cm and area of a triangle formed by dividing

this square into two equal halves is 1 sq. cm each.
2

A
B
C Area of square
D = 1 cm 2
E
H
F G Area of triangle
1
= 2 cm 2

Since, region A consists of 6 unit squares, its area is 6 cm . Find the area of other regions and
2
complete the following table.

Region A B C D E F G H Polygon
1
Area (cm ) 6
2
2
Thus, area of the polygon is _________ cm .
2
Can you find the perimeter of the above polygon?
One method is by putting a thread along all the sides of a polygon on a geoboard, straightening
the thread and measuring it with a ruler. The perimeter of the given polygon is greater than
20 cm. Why?

At a Glance

1. The perimeter of a closed figure is the length of its boundary.

2. Perimeter of some geometrical figures are as follows:
(a) Perimeter of a rectangle = 2 × (Length + Breadth)

(b) Perimeter of a square = 4 × (Length of its side)

(c) Perimeter of an equilateral triangle = 3 × (Length of its side)
(d) Perimeter of other closed figures formed by straight lines = Sum of its sides

3. The amount of surface or region enclosed by a closed figure is called its area.

4. Formulae to find areas of certain standard figures are given below:
(a) Area of a rectangle = Length × Breadth

(b) Area of a square = Side × Side

Area Area
(c) Length of a rectangle = ; Breadth of a rectangle =
Breadth Length

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