Given: Lines y and z are parallel, and ABC forms a triangle. Prove: m∠5 + m∠2 + m∠6 = 180° Lines y and z are parallel. Triangle A B C sits between the 2 lines with point A on line y and points C and B on line z. Angle C A B is 2. Its exterior angle to the left is 1 and its exterior angle to the right is 3. Angle A B C is 6 and its exterior angle to the right is 7. Angle B C A is 5 and its exterior angle to the left is 4. Statements Reasons 1. ABC is a triangle 1. given 2. y ∥ z 2. given 3. ∠1 ≅ ∠5; ∠3 ≅ ∠6 3. ? 4. m∠1 = m∠5; m∠3 = m∠6 4. def. ≅ 5. m∠1 + m∠2 + m∠3 = m∠LAM 5. ∠ addition postulate 6. m∠1 + m∠2 + m∠3 = 180° 6. def. Straight angle 7. m∠5 + m∠2 + m∠6 = 180° 7. substitution Which could be the missing reason in Step 3? alternate interior angles are congruent alternate exterior angles are congruent vertical angles are congruent corresponding angles are congruent

The correct option is;

Alternate interior angles

Step-by-step explanation:

The m∠5 + m∠2 + m∠6 = 180° proof is given as follows;

Statement                                        Reason

1. ABC is a triangle                           Given

2. y ║ z                                              Given

3. ∠1 ≅ ∠5; ∠3 ≅ ∠6                         Alternate interior angles

4. m∠1 = m∠5; m∠3 = m∠6               Definition of (congruency) ≅

5. m∠1 + m∠2 + ∠3 = m∠LAM          ∠Addition postulate

6. m∠1 + m∠2 + ∠3 = 180°                Definition of straight angles

7. m∠5 + m∠2 + ∠6 = 180°                Substitution property

Step 3;

Given that line y is parallel to line z, we have that the transversal AB will make equal corresponding angles with the lines y and z, therefore, ∠6 will be equivalent to segment AB extended

Which gives, ∠6 is supplementary to ∠a where ∠a = ∠1 + ∠2

Therefore, given that ∠3 is also supplementary to ∠a where as we have above, ∠a = ∠1 + ∠2, we have that ∠3 = ∠6 and ∠3 ≅ ∠6 where ∠3 and ∠6 are alternate interior angles;

Similarly, ∠1 ≅ ∠5 by alternate interior angles of two parallel lines property.

i think the answer is seven, for if i'm being useless °ω°

step-by-step explanation: