Statement Reason
1. Let points A, B, and Cform a
triangle
given
2. Let De be a line passing
through B, parallel to AC,
with angles as labeled
defining a parallel line and labeling angles
3.
4.m_1 = m 4, and
m23 = m25.
Congruent angles have equal measures.
5.m24+ m2 2 + m25 = 180°
angle addition and definition of a straight angle
6. m_1 + m22 + m23 = 180°
substitution
What is the missing step in this proof?