In triangle(XBC): since BX = CX, this triangle is isosceles.
Therefore, angle(XBC) = angle(XCB).
Since ABCD is a rectangle, angle(B) and angle(C) are right angles.
Therefore, angle(ABX) = angle(DCX).
Triangle(ABX) is congruent to triangle(DCX):by SAS, making AX = DX.
