Chapter 4.3, Problem 67ES

A rectangular plot of land is to be fenced off so that the area enclosed will be $400{\text{ ft}}^2$ . Let $L$ be the length of fencing needed and $x$ the length of one side of the rectangle. Show that $L=2x+800/x$ for $x>0,$ and sketch the graph of $L$ versus $x$ for $x>0$ .