INTRODUCTORY EXERCISES

(2) A farmer has 2400 ft of fencing and wants to fence off a rectangular field that borders a straight river. He needs no fence along the river. Express the area of the field as a function of the length of the side parallel to the river.

Let W = width of field
    L = length of field
    A = area of field

    2W + L = 2400  ==>  2W = 2400 - L  ==> W = 1200 - L/2
    A = LW

    A = L(1200 - L/2)
      = 1200L - L2/2

The area in terms of length is given by the formula:
    A = 1200L - L2/2