The Pythagorean theorem has a reciprocal variant:
![https://commons.wikimedia.org/wiki/File:Inverse_pythagorean_theorem.svg](https://www.futilitycloset.com/wp-content/uploads/2024/07/2024-07-19-inside-out-1.png)
In combination with the inverse-square law, this means that identical lamps placed at A and B will produce the same light intensity at C as a single lamp at D.
The Pythagorean theorem has a reciprocal variant:
In combination with the inverse-square law, this means that identical lamps placed at A and B will produce the same light intensity at C as a single lamp at D.