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Q.



As observed from the top of a 75 m high lighthouse from the sea-level, the angles of depression of two ships are 30° and 45°. If one ship is exactly behind the other on the same side of the lighthouse, what is the distance between the two ships?

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a

75 3 m  

b

75( 3 +1)m  

c

75( 3 1)m  

d

70( 3 1)m   

answer is C.

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Detailed Solution

Given that,
Angle of depression from the top of the lighthouse of the ship = 30 o  ,
Angle of depression from the top of the lighthouse of the ship = 45 o  .
Also, height of the lighthouse = 75 m.
The given situation is represented diagrammatically below,
Question Image
In ΔBCA,  
tan45= AB BC 1= 75 BC BC=75  
In ΔBDA,  
tan30= AB BD 1 3 = 75 BD BD=75 3  
The distance between the ships = BD – BC = CD.
CD=75 3 75 CD=75( 3 1)m  .
Therefore, the distance between the ships is 75( 3 1)m   at the given instance.
The correct option is 3.
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