1. From a point on a bridge across the river, the angles of depression of the banks on opposite sides of the river are 30° and 45° respectively. If the bridge is at a height of 2.5m from the banks, then the width of the river is (take √3 = 1.732)
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By: anil on 05 May 2019 01.48 am
AC is the height of the bridge = 2.5 m Width of river = BD = ? In $$ riangle$$ ACD, => $$tan(angle ACD)=frac{AC}{CD}$$ => $$tan(45^circ)=1=frac{2.5}{CD}$$ => $$CD=2.5$$ m Similarly, in $$ riangle$$ ABC, => $$tan(30^circ)=frac{2.5}{BC}$$ => $$frac{1}{sqrt{3}}=frac{2.5}{BC}$$ => $$BC = 2.5 imes 1.732 = 4.33$$ m $$ herefore$$ BD = BC + CD = $$2.5 + 4.33=6.83$$ m => Ans - (B)
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