A picture 5 feet in height is hung on a wall so that its bot-ton1.is 8 feet from the floor, as shown in Figure 9. A viewer with eye level at 5.4 feet stands b feet fron1 the wall. Express 0, the vertical angle subtended by the picture at her eye, in terms of b, and then find 0 if b = 12.9 feet.
It should be clear from the diagram that if
x = angle to bottom of picture
y = angle to top of picture
b tany - b tanx = 5
so, since θ = y-x,
tanθ = (tany - tanx)/(1 + tany tanx)
= (5/b) / (1 + (2.6/b)(7.6/b))
= (125b)/(25b^2 + 494)
Now just plug in b=12.9 and find θ