Question 1019001
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Prove the theorem that states that if AD/DB=AE/EC, then DE||BC
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The Theorem formulation is as follows:


   If in a triangle a straight line connects two sides and cuts off proportional segments in the triangle sides, 
   then this straight line is parallel to the third side of the triangle. 


See the lesson <A HREF=http://www.algebra.com/algebra/homework/Triangles/In-a-triangle-a-straight-line-parallel-to-its-side-cuts-off-a-similar-triangle.lesson>In a triangle a straight line parallel to its side cuts off a similar triangle</A> in this site, Theorem 2.
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