question_answer

A person standing on the bank of a river observes that the angle of elevation of the top of a tree on the opposite bank of the river is \[60{}^\circ \]and when he retires 40 m away from the tree, the angle of elevation becomes\[30{}^\circ \]. The breadth of the river is

A) 20 m 

B)                        30 m     

C)        40 m     

D)        60 m

Correct Answer: A

Solution :

The angle of elevation increases when the distance between the person and tree decrease (less). Letbe the height of the tree andbe the width of the river. Now, in                                                 ...(i) Now, in                                 [using Eq. (i)]