A.3 How do they differ?

Angles

Lines r and s are parallel. Alex finds the relationship between 3 and 5.

m3 = 70°

Alex's "Corresponding & Supplementary Angles" Method
3 and 7 are corresponding angles. Since 3 = 70°, then 7 is the same.
Because 7 and 5 add to 180°,
I know that
180° - 70° = 5.
3 and 5 add to 180°.
70° = 70°
180° − 70° = 110°
70° + 110° = 180°
m3 + m5 = 180°