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Area of the triangle = − − −
= 150 150 − 60 150 − 100 150 − 140
= 150 × 90 × 50 × 10
2
= 50 × 3 × 10 × 9 × 50 × 10

2
= 50 × 3 × 10 × 3 × 3 × 50 × 10

= (50× 10 × 3 3) 2

2
= 1500 3

Example-9

Find the cost of laying grass in a triangular field of sides 50 m, 65 m and 65 m at
2
the rate of Rs 7 per m .

Solution:

According to the question,

Sides of the triangular field are 50 m, 65 m and 65 m.

2
Cost of laying grass in a triangular field = Rs 7 per

Let a = 50, b = 65, c = 65

S= + + = 50+65+65 = 90 m.
2 2

So, Area of triangle = − − −

= 90 90 − 50 90 − 65 90 − 65

= 90 × 40 × 25 × 25

2
= 1500 m
2
Cost of laying grass = Area of triangle × Cost per m

= 1500×7

= Rs.10500

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