In the adjoining figure, explain how one can find the breadth of the river without crossing it.

Explanation

Let the breadth of the river be AB.
Mark a point M on the bank of the river at which B is situated.
Let O be the midpoint of BM.
From M move along `MN_|_BM` to a point N such that A, O, N are in the same straight line.
Then, `DeltaOBA~=DeltaOMN` and MN is the requrired breadth of the river.