In the Pythagorean theorem why do they refer to the sides of the right angle as the legs of the triangle? Who or where does this terminology come from?
I bet it's because most of the Western World learned their geometry from the Greeks first, who used the compass and straightedge for their geometry. To make right triangles with a compass, you could set it to a "L" shape...and stand it on it's "legs."
I don't think Pythagoras invented it because everyone from the Chinese to the Mayans had been using it forever. Perhaps he first proved it?
The Japanese learned their geometry with origami, so perhaps someone who knows Japanese will think of some other explanation...