Answer:
1. Given
2, Exterior sides on opposite rays
3. Definition of supplementary angles
4. If lines are ||, corresponding angles are equal
5. Substitution
Explanation:
For the first one, it is given as shown in the problem. Also in the figure you can see that line s is parallel to line t.
2. ∠5 and ∠7 are adjacent, they share a common side. Their non-common side are rays that go in a direction opposite of each other. Also you can see that they form a straight line, which means that they are supplementary.
3. Supplementary angles simply put are angles that sum up to 180°. You know this for sure because of proof 2, specifically the part that they form a straight line. The measure of a straight line is 180°.
4. Corresponding angles are congruent. These are angles that have the same relative position when a line is intersected by parallel lines. You have other example in the figure like ∠2 and ∠6; ∠3 and ∠7.
5. This is substitution because ∠1 substituted ∠5 in this case. Since ∠1 is equal to ∠5, then it can substitute it in the equation given in step 3. This means that ∠1 and ∠7 are supplementary as well.