Final answer:
The congruence of opposite sides in a quadrilateral does not determine specific relationships between diagonals without additional information.
Step-by-step explanation:
In quadrilateral ABCD, if sides AB and DC are congruent (AB≅DC) and sides AD and BC are congruent (AD≅BC), it does not necessarily imply any specific relationship between the diagonals AC and BD, such as being equal in length, being perpendicular to each other, bisecting each other, or forming a right angle just based on this information.
To identify a specific relationship, we would need additional information or constraints about the quadrilateral, like angle measures or if it adheres to a special category of quadrilaterals (e.g., parallelogram, rectangle, rhombus, or square).