Question

1.Ruth has 240 feet of fencing available to enclose a rectangular field. Express the area A of the rectangular field as a function x, where x is the length of the field.

2. For what value of x is the area largest?

3. What is the maximum area?

Answer 1

let the length be x
let the width be w
but 2x + 2w = 240
x + w = 120
w = 120-x

area = xw = x(120-x)
= -x^2 + 120x

d(area)/dx = -2x + 120
= 0 for a max of area
-2x = -120
x = 60
then w = 120-60 = 60

for the max area the rectangle should be a square of 60 ft by 60 ft
for a max area of 3600 ft^2