Puzzle

They are both right. It is true, as Mitchell says, that the adjoining wall, the left edge of the mirror, and the right edge of the mirror are all parallel. But Luanne is also right when she says that the right edge of the mirror is not vertical, although she must have very sharp eyes to notice it.

Vertical means pointing toward the center of the Earth. Let’s say we put up a tall building at the North Pole and another in western Africa, making sure that each is vertical. They are not parallel. Parallel lines are defined as lines that will never meet. If we follow the lines made by these two buildings, they meet at the center of the Earth.

In principle, the right edge of the mirror that Mitchell installed is not vertical if it is, as he says, parallel to the left edge and to the adjoining wall. But, the difference is very slight.

Hmmm . . . How far off vertical is the right edge of the mirror?