Vertical angles are the opposite angles where two lines cross. They are equal. Adjacent angles on the same line add to 180. Angle facts as a set are in lines and angles.
X marks the pair
The two angles that do not share a side are the vertical pair. If one is 70, the one across from it is 70. Complementary and supplementary sums are in complementary and supplementary angles.
Triangle interiors still add to 180, in triangle angle sum. The short list is in ACT Math formulas.
The bottom line
Opposite angles at a crossing: equal. Neighbors on a straight line: 180.
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