Table of Contents
Definition
Vertical Angles are the angles opposite each other when two lines cross
In this case, “Vertical” means they share the same corner point (Vertex), not the usual meaning of up-down.
Example
a° and b° are vertical angles.
Vertical Angles are Congruent Angles
The interesting thing here is that vertical angles are congruent angles:
a° = b°
they are equal
Example
Find angles a°, b° and c° below:
Because a° is vertically opposite 100°, it must also be 100°
A full circle is 360°, so that leaves 360° − 2×100° = 160°
Angles b° and c° are also vertical angles, so must be equal, which means they are 80° each.
Answer: a = 100°, b = 80° and c = 80°.