The perimeter of the rectangle is $\"P=20\"$ m.

Perimeter of a rectangle is $\"P=2(L+B)\"$ ,

where $\"L\"$ is the length of the rectangle.

$\"B\"$ is the breadth of the rectangle.

Find $\"B\"$ in terms of $\"L\"$ .

$\"20=2(L+B)\"$

$\"10=L+B\"$

$\"L+B=10\"$

$\"B=10-L\"$

Find the area of the rectangle in terms of $\"L\"$ .

Area of the rectangle is $\"A=L\\times$

Substitute $\"B=10-L\"$ in the area of the rectangle.

$\"A(L)=L\\times$

$\"A(L)=10L-L^2\"$ .

Domain :

The area of the function is $\"A(L)=10L-L^2\"$ .

All possible values of $\"L\"$ is the domain of the function.

Area of the rectangle should be a greater than zero.

$\"10L-L^2>0\"$

$\"L(10-L)>0\"$

$\"L>0\"$ and $\"10-L>0\\Rightarrow$ .

The domain of the function is $\"0<$ .

Area of the rectangle in terms of length $\"L\"$ is $\"A(L)=10L-L^2\"$ .

The domain of $\"A(L)=10L-L^2\"$ is $\"0<$ .