Optimize the Length of the Crease of a Folded Piece of Paper

A sheet of legal paper is 8.5 by 11.75 inches long. The lower-left corner is brought to a point inches from the upper-left corner and folded to form a crease. This Demonstration shows a graph of the crease length as a function of and a diagram of the folded paper. By moving the slider, you can estimate the length of the shortest and longest possible crease. The exact shortest possible crease () and the exact longest possible crease () may be determined by using Mathematica or traditional calculus techniques.