A man in a boat rowing away from a light house 100 m high takes 2 minutes to change the angle of elevation of the top of the light house from 60⁰ to 30⁰. Find the speed of the boat in metres per minute. [Use 
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Or
Two poles of equal heights are standing opposite to each other on either side of the road, which is 80 m wide. From a point between them on the road, the angle of elevation of top of the poles are 60⁰ and 30⁰ respectively. Find the height of the poles and the distances of the point from the poles.
ACB = 60⁰ and 
ADB = 30⁰
Let, the length of CD = x m
And the length of CB = y m
⇒ y = 57.73 m
⇒ x + y = 173 m
⇒ x = 115.27 m
Speed of the boat = Distance/Time
= 57.635 m/min
Or
AEB = 60⁰ and 
DEC = 30⁰
Let, length of BE = x m
And length of two equal poles = h m
Then, length of EC = 80 – x m
…(1)
…(2)
From eq (1) and eq (2)
80 – x = 3x
⇒ x = 20 m
h= 20√3 m
So, the length of BE = 20 m
length of EC = 80 – 20 m = 60 m
length of two equal poles = 20√3 m
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