Page 162 - Maths Class 05

Area of Triangle

If a square is divided along its diagonal, it forms right isosceles triangle.

1 cm = 10 mm

1 sq cm = 100 mm 2
5 cm 2
1 sq m = 10000 cm

1 sq km = 1000000 m 2

1 sq m = 1000000 mm 2
5 cm

To understand one of triangles, let us take a square of 5 cm edge.

If we divide it along diagonal, we will get two isosceles triangles.

2
2
Area of square of 5 cm edge = (side) = (5 cm) = 25 cm 2
We are also finding in the interior of square of 5 cm edge there are 25 small squares of
1 cm edge.

Now, on dividing, the two triangles obtained are of the same area by observation.

Area of each triangle = 10 squares of 1 cm edge + 5 half squares of 1 cm edge.
5
= 10 +
2

Unit of area is square of = 10 + 2.5 = 12.5 cm.

unit length/distance.
1
1
= (25) = (Area of square of 5 cm edge)
2 2
Relationship between Area and Perimeter
Rectangle of same area : To understand, let us take a rectangle of area 18 sq. cm.
18 = 2 × 9 = 3 × 6 = 6 × 3 = 9 × 2 = 18 × 1

(a)

All rectangles shown as (a), (b) and (c) have area

equal to 18 sq. cm. (b)
Rectangle of the Same Perimeter
(c)
To understand consider a rectangle of perimeter 18 cm.

We know, 18 = 2 (8 +1) = 2 (7 + 2) = 2 (6 + 3) = 2 (5 + 4)

= 2 (1 + 8) = 2 (2 + 7) = 2 (3 + 6) = 2 (4 + 5)

Mathematics-5 162