Angles, Parallel Lines & Polygon Angles

How the lesson starts: Angles, Parallel Lines & Polygon Angles

Remy's skate park
Welcome to Remy's skate park, angle ace! Remy is designing ramps, rails and crossing paths. Every design has angles, and some are missing from the plans. The good news? Angles follow a few simple rules, and those rules find any missing angle!
A straight rail: 180°
A straight rail makes a straight angle: 180°. When a ramp leans on it, it splits that 180° into two angles side by side. They're called supplementary angles. One is 68°, so the other is 180° − 68° = 112°. Supplementary angles always add to 180°.
Crossing rails
Two rails cross like an X, making four angles. Angles 1 and 3 are opposite each other. They're called vertical angles, and they're always equal. Why? Angle 1 plus angle 2 is 180°, and angle 3 plus angle 2 is 180° too. So angles 1 and 3 must match: 50° each!