Since AJ and BD are parallel to each other, therefore, <CBJ = <AJB. Both angles are alternate interior angles.
Thus, two sides, AJ and JB and an included angle, <AJB, of ∆AJB, are equal to two sides, BC and JB, and an included angle, <CBJ of ∆CBJ. Therefore, ∆AJB and ∆CBJ are congruent to each other by the SAS Congruence Theorem.
