We know that,
The Heron's formula for calculating the area of the triangle,
Area of triangle =
where, s is the semi-perimeter = half of the perimeter = 21 cm
and a, b and c are the sides of the triangle
Triangular sides of walls are, a = 18 cm, b = 10 cm, c = ?
s = (a b c)/2
21 = (18 10 c)/2
21 2 = 28 c
42 = 28 c
c = 14 cm
Area of a triangular wall =
= 21 cm2
Hence, Area of the wall of the park to be painted in colour = 21 cm2.