Thm 3-1: If 2 intersecting lines form congruent adjacent angles, then the lines are perpendicular.
Thm 3-2: If 2 sides of 2 adjacent acute angles are perpendicular, then the angles are complementary.
Thm 3-3: If one angle of a linear pair is a right angle, then the other angle is a right angle.
Example 1:
Given: Angle 1 is congruent to Angle 2
Conclusion: Measure of Angle 1 = measure of Angle 2.
Answer: Definition of Congruence