Given: Angle A and Angle B are complementary angles. Angle B and Angle C are complementary angles. Prove: The measure of Angle A = the measure of Angle C. 

Statements  Reasons 
1. Angle A and Angle B are complementary angles.  given 
2. Angle B and Angle C are complementary angles.  given 
3. The measure of Angle A + the measure of Angle B = 90 degrees.  Definition of Complementary Angles 
4. The measure of Angle C + the measure of Angle B = 90 degrees.  Definition of Complementary Angles 
5. The measure of Angle A + the measure of Angle B = the measure of Angle C + the measure of Angle B.  Transitive Property of Equality[^t43] 
6. The measure of Angle A = the measure of Angle C.  Subtraction Property of Equality [^t44] 