H
E
E
L
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M
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the two sides AE, ED are equal to the two sides BE, ED, and the base DF is equal to the base EF ;
therefore
the angle AED is equal to the angle BED. [I.8]
Therefore
each of the angles AED, BED is right; [I.Def.10]
therefore
GK cuts AB into two equal parts and at right angles.
