You are in a large gallery with a large rectangular painting hung high on a wall. Its lower edge is m feet above your eye level. Its upper edge is n feet above your eye level.

How far back should you stand to maximize your viewing angle, the angle from your eyes to the top and bottom of the painting.

While the problem implies that m & n are both greater than the height of your eye by using the word "above",  there is nothing to physically prevent m or n from being negative, so long as n>m.  If eye level = E, then for the case of n>E and m<E, the answer by inspection is x=0. with the viewing angle = 180 deg.   Not very easy to see this way though.

Posted by Kenny M on 2014-02-18 21:08:57