The relationships between angles formed by two parallel lines having a common a transversal include, alternate interior, vertically opposite, corresponding, alternate exterior, same side, interior and exterior
The correct option for the missing reason in step 3. is as follows;
Alternate interior angles are congruent
The reason the above option is correct is as follows:
The given parameters are;
Line y is parallel to line z
The figure ABC forms a triangle
The two column proof is presented as follows:
Statement Reason
1. ABC is a triangle 1. Given
2. lines y and z are parallel 2. Given
3. ∠1 is congruent to ∠5; ∠3 ≅ ∠6 3. Statement reason required
∠3 is congruent to ∠6
4. m∠1 = m∠5; m∠3 = m∠6 4. By definition of congruency
5. m∠1 + m∠2 + m∠3 = m∠LAM 5. By angle addition Postulate
6. m∠1 + m∠2 + m∠3 = 180° 6. Angles on a straight line
7. m∠5 + m∠2 + m∠6 = 180° 7. Substitution (property)
Required:
The reason for the statement ∠1 ≅ ∠5; ∠3 ≅ ∠6
Solution:
From the attached diagram for the question, we have that angle ∠1 and angle ∠5 on line AC and ∠3 and ∠6 on line AB are alternate interior on two parallel lines, and they are therefore, congruent.
Therefore
∠1 ≅ ∠5, and ∠3 ≅ ∠6 by alternate interior angles theorem which states that alternate interior angles, which are the pair angles formed in the inside face of two parallel lines crossed by a common and the common transversal but on either of the transversal, are congruent
Therefore, the missing reason in Step 3 is; Alternate interior angles are congruent