A.1 Why does it work?
Angles
Find the relationship between ∠1 and ∠3.
m∠1 = 85°
Alex's "Upper Supplementary Angles" Method
∠1 and ∠2 are supplementary, so I know that 180° - 85° = ∠2.
∠2 and ∠3 are supplementary, so I know that 180° - 95° = ∠3.
The measure of ∠1 is the same as the measure of ∠3.
180° − 85° = 95°
180° − 95° = 85°
85° = 85°
∠1 ≅ ∠3