Page 4 - ln1

s – b = (125 – 80) m = 45 m,

s – c = (125 – 50) m = 75 m.

Therefore, area of the park(A) = − − −
= 125 125 − 120 125 − 80 125 − 50
= 125 × 5 × 45 × 75
= 5 × 5 × 5 × 5 × 3 × 3 × 5 × 5 × 5 × 3
2
= 375 15m

Also, Perimeter of the park = AB + BC + CA = 250 m

Therefore, length of the wire needed for fencing = (250 m – 3 m) (to be left for gate) =
247 m.

So, the cost of fencing = Rs 20 × 247 = Rs 4940

Example-4

Find the area of an equilateral triangle with side „x‟ unit using Heron‟s formula.

Solution:

According to the question,

Each side of the equilateral triangle is „x‟ .

Let a = x, b = x and c = x

3
S= + + = + + =
2 2 2
So, Area of triangle = − − −

3 3 3 3
= − − −
2 2 2 2

3
= × × ×
2 2 2 2

= 3 sq. unit
2
4

4