The bird is spotted flying 6000 ft from a tower . The distance of the tower from the bird is 6000 ft. The height of the tower is 9000 ft because the observer spot the distance from the top of the tower at a distance of 9000 ft.
The illustration forms a right angle triangle. The adjacent side of the triangle is 6000 ft and the height or opposite side of the triangle is 9000 ft. Using tangential ratio the angle of depression from the bird to the observer can be found as follows.
