## Vertical Angles

## 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°.