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Q.

A straight highway leads to the foot of a 50 m tall tower. From the top of the tower, the angles of depression of two cars on the highway are 30°   and 60°  .  What is the distance between the two cars and how far is each car from the tower?


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a

57m, 28m, 86m

b

57.76m, 28.88m, 86.6m

c

57.76m, 28.86m, 86.9m

d

57.74m, 28.86m, 86.6m 

answer is D.

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Detailed Solution

Given that,
The angle of depression of the first car will be θ= 60 °  
The angle of depression of the second car will be ϕ= 30 °   The height of the tower will be h=50  m
Question ImageIn ΔPQR   ,
RQ (the distance from the first car to the tower) = x   PQ=the tower
Substituting the values in tanθ= height base  ,
tanθ= h x x= h tanθ  
Substituting θ  = 60 °   and h  = 50  m,
x= 50 tan 60 ° x= 50 3 [tan 60 ° = 3 ] x=28.86m   Thus, the distance from the first car to the tower will be 28.86  m.
In ΔPQS   ,
SR =y = the distance from the second car to the first car
SQ = the distance from the second car to the tower
x+y   = the distance SQ.
tanϕ= PQ SQ tanϕ= PQ RQ+SR tanϕ= h x+y x+y= h tanϕ  
Substituting ϕ  = 30 °   and h  = 50  m,
x+y= 50 tan 30 ° x+y= 50 1 3 [tan 30 ° = 1 3 ] x+y=50 3 x+y=86.6m   Thus, the distance from the second car to the tower will be 86.6  m.
Substituting x  = 28.86  m in x+y=86.6  m,
28.86m+y=86.6m y=86.6m-28.86m y=57.74m   Thus, the distance between the two cars will be 57.74m, the distance from the first car to the tower will be 28.86  m and the distance from the second car to the tower will be 86.6  m.
Therefore the correct option is 4.
 
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