Statement Reason
1. Let points A, B, and form 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 = m 5.
Congruent angles have equal measures.
5. m24+ m2 + m25 = 180°
angle addition and definition of a straight angle
6. m.1 m 2 + m23 = 180°
substitution
What is the missing step in this proof?
A
Statement: 24-25, and 21 - 23.
Reason: Alternate Interior Angles Theorem
Statement DE is parallel to AC
Reason: AB is a transversal cutting De and AC.
Statement: 1 - 4, and 23 - 25.
Reason: Alternate Interior Angles Theorem
Statement: 21 - 4, and 3 - 5
Reason: 41 and 4, and <3 and 5 are pairs of supplementary angles.
D