Answer:
Alternate exterior angles
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Step-by-step explanation:
The parallel lines are like the metal parts of a train track, so I'll just refer to these lines as "train tracks" from now on. Note how x and y are on the outside or exterior of the train tracks. At the same time, they are on opposite or alternate sides of the transversal line.
Since x and y are on the alternate sides of the tranversal line, and they are on the exterior of the train tracks, we have alternate exterior angles
