# Heron's Principle of Reflection/Examples/Journey to the River

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## Example of Use of Heron's Principle of Reflection

Mary, who is standing at a point $S$, wants to walk to the point $T$.

However, first she wants to take a drink of water from a river.

She wants to walk as short a distance as possible.

To what point on the riverbank should she walk?

## Solution

Imagine the point $T'$ which is $T$ reflected in the line taken by the river bank.

The point $P$ is that point on the river bank directly in line with $S$ and $T'$.

Or you can reflect $S$ in the line taken by the river bank to get point $S'$.

Then $P$ is the point on the river bank directly in line with $S'$ and $T$.

## Sources

- 1992: David Wells:
*Curious and Interesting Puzzles*... (previous) ... (next): Light Reflected off a Mirror: $18$