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© Copyright 2003, Jim Loy
Below is a carpenter's square, which is held against the two dark red points. You can move the bright red point, and it moves in a curved path. Question: What is the shape of the curved path of this point? The answer is below:
Answer:
The curved path is a semicircle, as proved by Euclid. The above angle (made by the carpenter's square) is a right angle. Euclid's theorem concerned all angles, each of which forms a different circular arc. Only the right angle forms a semicircle.
The above Java interactive demonstration was created with Cinderella (a geometry program).
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