Chapter 4: Q9 E (page 238)
Consider the following problem: A farmer with 750 ft of fencing wants to enclose a rectangular area and then divide it into four pens with fencing parallel to one side of the rectangle. What is the largest possible total area of the four pens?
(a) Draw several diagrams illustrating the situation, some with shallow, wide pens and some with deep, narrow pens. Find the total areas of these configurations. Does it appear that there is a maximum area? If so, estimate it. (b) Draw a diagram illustrating the general situation. Introduce notation and label the diagram with your symbols.
(c) Write an expression for the total area.
(d) Use the given information to write an equation that relates the variables.
(e) Use part (d) to write the total area as a function of one variable.
(f) Finish solving the problem and compare the answer with your estimate in part (a).
Short Answer
(a) The diagrams for each case are shown, and the maximum area is \(12500\;{\rm{f}}{{\rm{t}}^2}\).
(b) The required diagram is shown where\(x\)and\(y\) be the width and depth of the rectangle in feet.
(c) The expression is \(A = xy\).
(d) The required equation is \(5x + 2y = 750\).
(e) The expression of area as a function of one variable is \(A\left( x \right) = 375x - \frac{5}{2}{x^2}\).
(f) The maximum value is obtained by closed interval method as \(A\left( {75} \right) = 14062.5\;{\rm{f}}{{\rm{t}}^2}\).