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, <span>Triangle AXB is congruent to triangle CXD.</span>