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 3 m from the banks, find the width of the river.

Explanation

Angle of depression of the banks on opposite sides of the rivers are `30^circ and 45^circ` respectively.
Let us label the banks A and B.
AB is width of the river. P is the point of observation.
Let PD denote the height of the bridge which is given as `3m`. D is a point lying on AB so
`/_PDA and /_PDB` are `90^circ`
Horizontal line passing through point P is parallel to AB. So
`/_PAB = 30^circ` and `/_PBA = 45^circ` as they are corresponding to the angles of depression.
angle of depression from P of point A = angle of elevation of P from A.
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