Question

A neighbor farmer had some chickens. She had 24 feet of wire fencing to

make a rectangular pen for the chickens. What different dimensions could
she use to build the pen if the perimeter remains fixed?

Answer 1

A rectangle is defined by its length = L, and its width = W.

So the perimeter of the of the rectangle can be written as:

Perimeter = 2*L + 2*W.

In this case, we want to leave the perimeter fixed, so we have:

24ft = 2*L + 2*W.

Now, we do not have any other restrictions, so to know the different dimensions now we can write this as a function, by isolating one of the variables.

2*L = 24ft - 2*W

L = 12ft - W.

or:

L(W) = 12ft - W.

Such that:

W must be greater than zero (because we can not have negative or zero width).

And W must be smaller than 12ft (because in that case we would have zero or negative length)

Then the possible different dimensions are given by:

L(W) = 12ft - W

0ft < W < 12ft.