Answer:
supplementary angles
Explanation:
1.) angle 1& angle 2 is supple. angle 2 & and angle 3 is supple.; given
2.) measure of angle 1+ measure of angle 2= 180, measure of angle 2+ measure of angle 3=180; Def. of Supple.
3.) measure of angle 1+ measure of angle 2 = measure of angle 2+measure of angle 3; Transitive
4.) measure of angle 1= measure of angle 3; Subtraction prop. of equality
5.) measure of angle 1 is congruent to measure of angle 3; Def. of Congruence