Answer:
5. ∠1.
6. ∠3.
7. ∠1.
8. 180°.
note: wherever there is a ∠ symbol, it means "angle".
Explanation:
5. An exterior angle of the triangle is ∠1.
6. The remote interior angles of the triangle to the exterior angle 1 are ∠2 and ∠3.
7. The sum of the measure of angles 2 and 3 is equal to the measure of ∠1.
8. The sum of the measure of angles 1 and 4 is 180°.
note: wherever there is a ∠ symbol, it means "angle".