Given m<1 + m<2 = 180° and m<2 + m<3 = 180°,
which reason justifies line 3 in the proof below
that <1=<3?
1: m<1+ m<2 = 180°
2: m<2+ m<3 = 180°
3: m<1+ m<2 = m<2 + m <3
m<3
4: m <1=m<3
5:<1=<3
A. Angle Addition Postulate
B. Defn. of Supplementary Z's
C. Defn. of Congruence
D. Substitution Property​