and the distance between the two buildings is also m. Example : From a point on a bridge across a river, the angles of depression of the banks on opposite sides of the river are ° and °, respectively. If the bridge is at a height of m from the banks, find the width of the river. Solution : In Fig .
, 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 the bridge at a height of m, i.e., DP = m. We are interested to determine the width of the river, which is the length of the side AB of the D APB. AB = AD + DB In right APD, A = °.
tan ° = PD AD Fig. . = AD or AD = m Also, in right PBD, B = °. So, BD = PD = m.