Vertical Angles

When 2 lines intersect, they form 4 angles:

Vertical angles are angles that are opposite each other:

Consecutive pairs of angles form a line, so they add to 180^o. They are called a linear pair. If one angle measures 30^o, then its adjacent angles measure 180^o − 30^o = 150^o, so they are equal. Likewise if an angle measures 150^o, then its adjacent angles measure 30^o, so they are equal. In other words, we have gone in a circle, and vertical angles will always be equal.

 

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