The value of θ = 12.40°
The angle of depression of the line of sight is the angle, θ, that the line of sight makes with the horizontal, as shown in the figure to the right.
Since the ground is level, it is parallel to any horizontal line, and so the angle that the line of sight makes with the ground is equal to θ as well.
As a result, we have
tanθ= 12.6/58.5
θ= tan-1 (12.6/58.5)
θ= tan-1 (0.22)
θ= 12.40°
Complete question:
A person stands at the window of a building so that his eyes are 12.6 m above the level ground in the vicinity of the building. An object is 58.5 m away from the building on a line directly beneath the person. Compute the angle of depression of the person’s line of sight to the object on the ground.