Question 1010570
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Given AD= BC and AB = CD
Prove triangle CDB is congruent  To triangle ABD
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Apply SSS-test for triangles.


You can also look into the lesson <A HREF=http://www.algebra.com/algebra/homework/Parallelograms/Properties-of-the-sides-of-a-parallelogram.lesson>Properties of the sides of a parallelogram</A> in this site, Theorem 2:


&nbsp;&nbsp;&nbsp;&nbsp;If in a convex quadrilateral the opposite sides are of equal length by pairs, &nbsp;then the quadrilateral is a parallelogram.