Making TrianglesDate: 11/12/2001 at 14:29:56 From: David Subject: Demonstrating triangles I've been trying to find ways to demonstrate a triangle that contains 180 degrees without using a protractor. -Dave Date: 11/12/2001 at 15:50:27 From: Doctor Peterson Subject: Re: Demonstrating triangles Hi, David. Here's a simple way to demonstrate what you want. Three angles that add up to 180 degrees can be put together to form a straight angle (a line): \ / \ / a\b/c ------+------ So make a triangle out of paper, tear off the three corners, and fit them together this way. They should always form a straight line. Or, to make a more impressive demonstration that comes close to a geometrical proof, place your triangle so that angles a and c are both acute (b may be obtuse), and fold the corners in (dividing two edges in half) so they all meet on the remaining edge: + / b \ / \ / \ / fold \ +-------------------+ /|f f| \ / |o o| \ / |l l| \ /a |d d| c \ +----+-------------------+--------------+ +-------------------+ |\ / | | \ / | | \ / | | a\ b /c | +----+--------------+ You will end up with a rectangle surrounding three angles that together form its bottom edge: 180 degrees. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
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