[OT] Fw: Re: [Fwd: Re: Need help in interpreting symbol 225e (measured by)]

From: Philippe Verdy (verdy_p@wanadoo.fr)
Date: Mon Mar 13 2006 - 19:56:05 CST

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    From: "Mike Ayers" <mayers@celequest.com>
    > Minor correction:
    > http://whyslopes.com/Euclidean-Geometry-Introduction/geom02_Isometry.html

    You say in this document:
    "The side-angle-side method fails when the angle > a straight angle"
    In fact, the angle can be any value for any triangle specified by the length of two of its sides, and the angle formed by these sides (SAS method), including obtuse angles, or outer and negative angles...
    See http://whyslopes.com/Euclidean-Geometry-Introduction/geom08_Side_Angle_Side_Failure.html

    May be you wanted to say:
    "The side-angle-side method fails when the angle > two straight angles"
    to forbid outer angles, as they are equivalent to the negation of their complement to two straight angles...
    But then you could also restrict to positive or null inner angles (because it's enough to swap the two sides to get a positive angle for an isometric triangle...

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