How to find the width of river by using triangle congruence

1. Choose a reference A on the other side of the river.

2. Choose a point B on this side of the river to make AB perpendicular to the river, and AB is the width of the river.

3. Choose two points C and D by the river to make BC=CD.

4. Visually draw a straight line AC, which intersects the vertical line of BD at E,

5. The length of the measure is the width of the river.

Prove:

At △ABC and △EDC,

∠AB=∠EDC=90，

BC =DC,

∠ACB=∠ECD，

∴△ABC≌△EDC(ASA)，

∴AB=DE.