Complete the proof that when a transversal crosses parallel lines, corresponding angles are congruent. This proof uses the following theorem: When a transversal crosses parallel lines, alternate interior angles are congruent. Statement Reason 1 AC | DF Given. 2 m/w+m/x - 180 These angles form a linear pair. 3 mzy+mZz -180 These angles form a linear pair. 4 m/w+ mzx V Substitution (2, 3). 5 mZx - mZy Alternate interior angles of parallel lines are congruent 6 myw+m/x Substitution (4, 5). 7 m/w = mzz Subtract myx from both sides of the equation (6)