The Nearsighted Cow Problem: A Calculus Classic.

A rectangular billboard 6 feet in height stands in a field so that its bottom is 10 feet above the ground. A nearsighted cow with eye level at 4 feet above the ground stands feet from the billboard. Express , the vertical angle subtended by the billboard at her eye, in terms of . Then find the distance the cow must stand from the billboard to maximize .

= is maximized when =

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You can earn partial credit on this problem.