Question

From a point on a bridge across a river, the angles of depression of the banks on opposite sides of the river are 30º and 45º respectively. If the bridge is at a height of 3m from the banks, find the width of the river.

Answer 1

In Fig. 11,27, A and B represent points on the bank on opposite sides of the river so that AB is the width of the river. P is a point, on a bridge at a height of 3m, i.e, DP = 3m. We are interested to determine the width of the river, which is the length of the side AB of the ΔAPB.