Khan/khan-exercises — Issue #8609: Quadrilateral types - "Quadrilateral" in Quadrilateral Types module cannot exist in Euclidean geometry as shown
Author: KhanBugz
Created: 2011-12-14 04:06:20+00:00
State: open
Labels: safari, snowleo, wrong-or-unclear

Reporter: mwholz65432@gmail.com

In the section on Quadrilateral Types, a figure ABCD is shown. The length of side AB is 4.4, BC is 2.3, CD is 4.5 and DA is 2.3. The angle (in degrees) of DAB is 88, ABC is 96, BCD is 84 and CDA is 92.

Since the sum of angles DAB and CDA is 180 then AB and CD are parallel. This along with the fact that sides BC and DA have the same length, mean that angle DAB and BCD are equal and, similarly, that ABC and CDA are equal. The figure shown has unequal values for these angles where Euclidean geometry dictates that they are equal.

I don't believe that the Khan Academy has tackled non-Euclidean geometry yet.

I took a screen shot of the erroneous problem and I will be happy to provide it upon request.

[quadrilateral_types.html?seed=108&problem=square](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/quadrilateral_types.html?seed=108&problem=square&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/quadrilateral_types.html?seed=108&problem=square&debug&activity=%5B%5D)

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