Page 7 - ln1

Area of the triangle,

=

= 21(21 – 18) (21 – 10) (21 – 14) cm 2

2
= 21 × 3 × 11 × 7cm
2
= 21 11 cm

Example-8

Sides of a triangle are in the ratio of 3: 5 :7 and its perimeter is 300cm. Find its
area.

Solution:

The ratio of the sides of the triangle is given as 3: 5: 7

Now,a:b: c= 3: 5: 7

∴a = 3x , b = 5x and c = 7x

It is also given that the perimeter of the triangle = 300cm

3x + 5x + 7x = 300

⇒ 15x = 300

⇒ x = 20

Now, the sides of triangle are 3x= 3 × 20 = 60

5x= 5 × 20 = 100

7x= 7× 20 = 140

So, the semi perimeter of the triangle (s) = 300 = 150 cm
2

Using Heron‟s formula,

7