Definition:Triangle (Geometry)

Definition

 * Triangle.png

A triangle is a polygon with exactly three sides.

Thus a triangle is a $2$-simplex.

Because it is a polygon, it follows that it also has three vertices and three angles.

Also known as
The word trigon can occasionally be seen, but this is rare.

Also see

 * Area of Triangle

Technical Note
The $\LaTeX$ code to generate $\triangle ABC$ is written.

Note that  is not to be used, as, although producing a symbol similar in shape, this is actually the uppercase Greek letter delta: $\Delta$