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Discussion: Types of Triangles tpow
Topic: Isosceles?
Related Item: http://mathforum.org/mathtools/tool/18196/


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Subject:   RE: Isosceles?
Author: Annie
Date: Apr 7 2006
On Apr  7 2006, Oscar@MU wrote:
> I think that the sketch included in the Types of Triangles problem
> of the week has a problem. The red triangle seems to be isosceles,
> and it is, but students would disagree when they see the measures of
> the lengths of the sides. The lengths that should appear equal seem
> not to be, although they are close. The reason is that the display
> for one of the lengths was set to units, and the other to
> hundredths, hence making the numbers, as displayed, different. This
> create an interesting situation, in which a triangle has congruent
> angles, and yet the sides aopposite to these angles are not
> congruent!

Hi, Oscar.  I'm the author of the sketch.  I have to admit that I'm not seeing
the same problem you are.  I've downloaded the sketch on two different computers
and also looked at my original sketch, and all three sides of the red triangle
seem to be measured in hundredths.  I get 5.96 cm for both legs if I don't move
anything after I open the sketch.

I am curious at to whether anyone else is seeing the same behaviour that Oscar
does.  Please post a reply here if you are (or aren't, I guess).  Thanks.

Of course, rounding measurements and calculations in Sketchpad can lead to some
very interesting class discussions exactly because of the situation you describe
- things that you KNOW are equal don't seem to be, and how could that be?
:-)

        -Annie

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