Question

from the point on the ground, the angle of elevation to the top and bottom of the flagpost which stands on a building are 45° and 30° respectively. if height of the flag post is 15 metre find the height of the building​

Answer 1

Answer:

Let A be the point of observation and B be the foot of the building.

Let BC denote the height of the building and CD denote height of the flag post.

Given that ∠CAB=45  

∘

,∠DAB=60  

∘

 and CD=10m

Let BC=h metres and AB=x metres.

Now, in the right angled △CAB,

tan45  

∘

=  

AB

BC

​  

.

Thus, AB=BC   i.e., x=h                    (1)

Also, in the right angled △DAB,

tan60  

∘

=  

AB

BD

​  

 

⇒AB=  

tan60  

∘

 

h+10

​  

⇒x=  

3

​  

 

h+10

​  

                    (2)

From (1) and (2), we get   h=  3 h+10 ⇒  3

h−h=10 ⇒h=(  3−1 10

(3+1  )

3+1 )=  3−1

10(  3  +1)

​  

 

=5(2.732)=13.66m

Hence, the height of the building is 13.66m.

Explanation:

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