Question
A moving boat is observed from the top of a 150 m high cliff moving away from the cliff. The angle of depression of the boat changes from 60° to 45° in 2 minutes. Find the speed of the boat in m/h.
Solution
Let the distance BC be x m and CD be y m.
In ∆ABC,
In ∆ABD,
Using (1), we get 
Time taken to move from point C to point D is 2 min = 2/60 h=1/30 h.
Now,
In ∆ABC,
In ∆ABD,
Using (1), we get
Time taken to move from point C to point D is 2 min = 2/60 h=1/30 h.
Now,
