Answer :
The answer is: AAS
Proving that two triangles are congruent by AAS can be verified when two angles and a non-included side in the first triangle are equal to their corresponding two angles and non-included side in the second triangle.
For the given parallelogram (check attachment):
angle AXB = angle CXD (opposite angle)
angle ABX = angle CDX (alternate angles)
AB = CD (opposite sides in parallelogram are equal)
Therefore,
Triangle AXB is congruent to triangle CXD.
Proving that two triangles are congruent by AAS can be verified when two angles and a non-included side in the first triangle are equal to their corresponding two angles and non-included side in the second triangle.
For the given parallelogram (check attachment):
angle AXB = angle CXD (opposite angle)
angle ABX = angle CDX (alternate angles)
AB = CD (opposite sides in parallelogram are equal)
Therefore,
Triangle AXB is congruent to triangle CXD.
