revk, (edited ) Ok just saw this...
Pythagorus theorem but with regular hexagons not squares.
Took me a second, but obviously it is true, as area of a regular hexagon is just a constant times the square.
Cool though.
"The area of the equilateral triangle* of the hypotenuse is equal to the sum of the areas of the equilateral triangle* of the other two sides. *:any regular polygon"