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If the bridge is at a height of 9 meter from the banks then find the width of the river?

+1 vote

From a point on a bridge across a river, the angles of depression of the banks on opposite sides of the river are 60 degree and 45 degree respectively.
If the bridge is at a height of 9 meter from the banks then find the width of the river?
Assume both the banks are at same ground level.

posted Mar 13, 2019 by Swati Arora

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1 Answer

0 votes

14.2 m

See picture below:

enter image description here

AB is the widh of the river and = AD+DB
AD/DC=tan(45) => AD=9*tan(45)=9*1=9 m
DB/DC=tan(90-60) => DB= 9*tan(30)=9*0.58=5.2 m
AB=9+5.2=14.2 m

answer Mar 13, 2019 by Hanifa Mammadov

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