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.
Using calculus i've got d= SQRT(m*n), units immaterial , as long as they are the same.
Not able to provide explanation now, maybe later if no one does b4 me.