Question 2 • Pretest
In a parallelogram, the diagonals bisect each other, so AM = CM and BM = DM. The perpendicular diagonals make the four angles at M right angles, and the triangles share diagonal segments. Thus the four small triangles are congruent by side-angle-side. Their corresponding outer sides are equal, so all four sides of ABCD are equal and the parallelogram is a rhombus.
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