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Q.

An observer, 1.7 m tall, is 20 3   m away from a tower. The angle of elevation from the eye of observer to the top of tower is 30 °  . Find the height of tower.

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a

25.0 m

b

20.0 m

c

30.0 m 

d

21.7 m

answer is B.

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Detailed Solution

Given that an observer, 1.7 m tall, is 20 3   m away from a tower. The angle of elevation from the eye of observer to the top of tower is 30 °  .  We have to find the height of the tower.
In a right-angle triangle tanθ=  Opposite side   Hypotenuse   
Consider has the height of the tower.
Question ImageSo,
AB=h  and AE=h1.7  .
And,
BC=DE=20 3  
In ADE,E= 90 °   Therefore,
cos 30 ° = h1.7 20 3 1 3 = h1.7 20 3 h1.7 =20 h =20+1.7 Therefore, h=21.7 m  
The height of the tower is h = 21.7m.
Therefore, the correct option is 2.
 
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