Arectangular billboard 8 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 x feet from the billboard. express θ, the vertical angle subtended by the billboard at her eye, in terms of x. then find the distance x(0) the cow must stand from the billboard to maximize θ.

find θ(x) and

θ is maximized when x0＝？