The upper right-hand corner of a piece of paper, 12 in. by 8 in., as in the figure, is folded over to the bottom edge. How would you fold it so as to minimize the length of the fold? In other words, how would you choose x to minimize y?

Answer 1

I must be missing something. Clearly the minimum length of fold is achieved when the paper is folded in half, so the upper right corner touches the lower right corner. Then the fold is straight across, and is 8" long. Any diagonal fold will be longer.

Of course, I have no diagram, so I don't know whether the paper is portrait or landscape orientation.