# Vertical Angles

**Vertical Angles** are the angles opposite each other when two lines cross

"Vertical" in this case means they

**share the same Vertex**(corner point), not the usual meaning of up-down.

### Example: a° and b° are vertical angles.

The interesting thing here is that **vertical angles are equal**:

a° = b°

(in fact they are congruent angles)

Have a play with them yourself. Notice how the 4 angles are actually **two pairs** of "vertical angles":

images/geom-vert-angles.js

### Example: Find angles a°, b° and c° below:

Because b° is vertically opposite 40°, it must also be 40°

A full circle is 360°, so that leaves 360° − 2×40° = 280°

Angles a° and c° are also vertical angles, so must be equal, which means they are 140° each.

Answer: **a = 140°**,** b = 40° and c = 140°**.

Note: They are also called Vertically Opposite Angles, which is just a more exact way of saying the same thing.

2121, 2122