What is the relationship between the triangles in figure 1?

Figure 1:

• The diagonals of quadrilateral ABCD intersect at a point, let's call it O.
• The markings on the diagonals indicate that the segments AO = OC and BO = OD.
• This condition, where the diagonals bisect each other, is a characteristic property of a parallelogram.

Answer: The triangles formed by the diagonals are congruent, and the quadrilateral is a parallelogram.