Nothing much to do with Pythagoras, but that triangle in the foreground is compelling, notwithstanding that it's a bit ragged on the longest side. Anyway, for reference:
The square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides.
Canon EOS 40D + Canon EF 35-135mm f/4-5.6 lens.