2. complete the proof of the exterior angle theorem

The correct answer is:

1. Because of collinearity and supplementarity-

2. They remain along the same line.

3. The sum of them is 180 degrees.

4.  Supplementarity.

5. The sum of the internal angles of a triangle is 180ª  

6. Supplementarity and external angle theorem sum up the same.

7.  Nothing.

Step-by-step explanation:

1. The reason why the exterior angle of 3 is 4, its because the last one is supplementary and collinear to the other.

2. Angle 3 and 4, form a collinear pair since they remain along the same line.

3. Angle 3 is supplementary to 4 because the sum of them is 180 degrees.

4.  The sum of the angles are 3 and 4 is 180 because they are supplementary.

5. The sum of the angles mentioned is: 180  because of internal angle theorem.

6.  It's like that because supplementarity and external angle theorem sum up the same. i.e, angle 1 + angle 2 + angle 3  = angle 3 + angle 4 =180

7. Nothing.