During Van Mahotsav, some children planted trees in a triangular region, two sides of which are 18 m and 10 m and the perimeter is 42 m. Find the area of the planted region.

The correct answer is: 21√11 m2

Let a = 18 m , b = 10 m and third side = c
It is given that Perimeter of triangle = 42 m
a + b + c = 42
18 + 10 + c = 42
c = 42 – 28 = 14 m
Using Heron’s formula,
Area of triangle =  where s = 
s =  = 21
Area of triangle = 
=