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Question:

When two lines intersect, adjacent angles are ____ (they add up to 180°) and angles across from either other are ____ (they're equal).

A supplementary, vertical
Explaination

Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are supplementary (they add up to 180°) and angles across from either other are vertical (they're equal).