Answer:
The required drawing showing the cliff, river, and tower as well as the details in the question is attached, please find alongside the answer
The width of the river is approximately 51.55 meters
Step-by-step explanation:
The height of the observation tower = 11 meters
The angle of elevation of the cliff top and the opposite side of the river = 20°
The angle of elevation of the tower top and the opposite side of the river = 30°
Therefore, by sine rule, we have;
h/sin(20) = w/sin(60)
11/sin(10) = length, l/sin(60)
l = sin(60) ×11/sin(10) ≈ 54.86 meters
w = l × cos (20) = 54.86 meters × cos (20) ≈ 51.55 meters
The width, w, of the river is approximately 51.55 meters.
