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Q.

The two palm trees are of equal heights and are standing opposite each other on either side of the river, which is 80 m wide. From a point O between them on the river the angles of elevation of the top of the trees are 60° and 30°, respectively. Find the height of the trees.


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a

Height = 34.6 m and the distance of point O from the tress is 20m and 60m.

b

Height = 24.6 m and the distance of point O from the tress is 20m and 60m.

c

Height = 34.6 m and the distance of point O from the tress is 30m and 30m.

d

Height = 34.6 m and the distance of point O from the tress is 20m and 50m. 

answer is A.

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Detailed Solution

Given that, the two palm trees are of equal height and stand opposite one other on opposite sides of the 80-meter-wide river.
The angles of elevation of the tops of the trees are measured from a point O on the river between them are 60 °   and 30 °   respectively.
Question ImageLet BC = river, AB = CD = palm tree = h and,
OB = x, then OC = 80 – x.
We can observe that, in ΔABO  
tan 60 ° = h x 3 = h x 3 x=h.............(1)  
In ΔCDO  ,
tan 30 ° = h 80x 1 3 = h 80x .............(2)  
Substitute eq (1) in (2).
We get,
1 3 = 3 x 80x 80x=3x 4x=80 x=20  
Therefore,
h = 3x =34.6 m   Now, let us find the height of the trees.
BO =x=20m DO =80x =8020 =60 m  
Height of the trees = 34.6 m and the distance of point O from the tress is 20m and 60m.
The correct option is (1).
 
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