# There is a slide in a park. One of its side walls has been painted in some colour with a message “KEEP THE PARK GREEN AND CLEAN” (see Fig. 12.10). If the sides of the wall are 15 m, 11 m and 6 m, find the area painted in colour.

**Solution:**

Given: Dimensions of the triangular wall.

By using Heron’s formula, we can calculate the area of a triangle.

Heron's formula for the area of a triangle is: Area = √s(s - a)(s - b)(s - c)

Where a, b and c are the sides of the triangle, and s = Semi-perimeter = Half the perimeter of a triangle.

The sides of the triangular walls are a = 11 m, b = 6 m and c = 15 m.

Semi Perimeter:

s = (a + b + c)/2

= (11 + 6 + 15)/2

= 32/2

= 16 m

By using Heron’s formula,

Area of triangular wall = √s(s - a)(s - b)(s - c)

Substituting the given values in formula,

= √16(16 -11)(16 - 6)(16 -15)

= √16 × 5 × 10 × 1

= √800 m²

= 20√2 m²

Area of the wall of the park to be painted in colour = 20√2 m^{2}.

**Video Solution:**

## There is a slide in a park. One of its side walls has been painted in some colour with a message “KEEP THE PARK GREEN AND CLEAN” (see Fig. 12.10). If the sides of the wall are 15 m, 11 m and 6 m, find the area painted in colour.

### Class 9 Maths NCERT Solutions - Chapter 12 Exercise 12.1 Question 3:

**Summary:**

It is given that there is a slide in a park. One of its side walls has been painted in some colour with a message “KEEP THE PARK GREEN AND CLEAN”. The sides of the wall are 15 m, 11 m and 6 m and we have found that the area painted in colour 20√2 sq. m.