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manish singh

· started a discussion

· 1 Months ago

no diagram (Question: 111090.0 )

you are using notations a,b,c,d but without the diagram how one will be able to understand.........instead don't give solution very bad impression

Question:

A person standing on the bank of a river observes that the angle of elevation of the top of a tree standing on the opposite bank is 60o. When he moves 20 meters away from the bank, he finds the angle of elevation to be 30o. The width of the river are.

      
Options:
A) 10 m
B) \(10\sqrt[]{3}\) m
C) 20 m
D) \(20\sqrt[]{3}\) m
Solution:
Ans: (a)


In ΔCAB,
Tan 60o = h / x
⇒ √3 = h / x.
⇒  h = √3x -----(i)
In ΔDAB,
Tan 30o = h / (20 + x)
⇒ 1 / √3 = h / (20 + x)
⇒  (20 + x) = √3h -----(ii)
Substituting h = √3x  in equation (ii)
⇒  (20 + x) = √3x√3x
⇒  (20 + x) = 3x
2x = 20
x = 10.
There fore ,width of the river = 10 meters

Abhinav Sinha

· commented

· 1 Months ago

Dear student
We have updated the question and solution both,
please solve it again.

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