You are standing in front of a mirror. Your shoulder width is 50 cm and your eyes are 6 cm apart. What is the minimum mirror width for a stereo view of yourself?

Solution

The minimal mirror width is 28 cm.

By careful inspection of the reflection of left and right shoulder tip in left and right eye, we construct the above diagram. It is seen that for mono vision we need only 22 cm mirror width. For a stereo view an extra 6 cm is needed.