# Definition:Polygon/Base

## Definition

For a given polygon, any one of its sides may be temporarily distinguished from the others, and referred to as the **base**.

It is immaterial which is so chosen.

The usual practice is that the polygon is drawn so that the **base** is made horizontal, and at the bottom.

For polygons of particular types, the following specific definitions can be made:

### Base of Triangle

For a given triangle, one of the sides can be distinguished as being the **base**.

It is immaterial which is so chosen.

The usual practice is that the triangle is drawn so that the **base** is made horizontal, and at the bottom.

In the above diagram, it would be conventional for the side $AC$ to be identified as the **base**.

### Base of Isosceles Triangle

The base of an isosceles triangle is specifically defined to be the side which is a different length from the other two.

In the above diagram, $BC$ is the **base**.

### Base of Parallelogram

In a given parallelogram, one of the sides is distinguished as being the **base**.

It is immaterial which is so chosen, but usual practice is that it is one of the two longer sides.

In the parallelogram above, line $AB$ is considered to be the **base**.