From a point on a bridge across a river, the angles of depression of the banks on opposite sides of the river are 60° and 45° 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.
OPtion
1) 14.02 m
2) 14.11 m
3) 14.20 m
4) 14.40 m
5) 14.73 m
6) 14.35 m
7) 14.05 m
8) 14.53 m
9) 14.63 m
10) None of these
Solution
Let A and B be the two sides of the river and C be the point on the bridge. D is a point on straight line between A and B such that CD = 9 meters
Width of the river would = AD+BD
In right angled triangle ACD,
tan 60° = CD/AD
=> √3 = 9/AD
=> AD = 9/√3 = 3√3
In right angled triangle BCD,
tan 45° = CD/BD
=> 1 = CD/BD
=> CD = BD = 9 meters
So the width of the river is AD+BD = 9+3√3 = ~14.20 meters