Interesting stamp, Germany, 1.70 Euro.
@rgx You know what's interesting and relevant about this puzzle is that the lengths of the triangles are Fibonacci numbers.
@rgx If you move on along to right triangles with longer lengths that are still consecutive Fibonacci numbers, you can repeat this puzzle with a single square missing among larger right triangles, e.g. make the blue right triangles of leg lengths 3, 8, and 5, 13 respectively, then you would have a rectangular areas of size 40 and 39, because F₂F₄ - F₁F₃ = 1 for all consecutive Fibonacci numbers F₁, F₂, F₃, and F₄.
@rgx And the illusion, of course, works because the slope approaches the square of the golden ratio.
@clacke Wonderful explanation, thank you! 😃
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