Perimeter of Triangle

Theorem
Let $ABC$ be a triangle.

Then the perimeter $P$ of $ABC$ is given by:
 * $P = a + b + c$

where $a, b, c$ are the lengths of the sides of $ABC$.

Proof
The perimeter of a plane geometric figure is defined as the total length of the boundary.

By definition, the boundary of a triangle comprises the three sides of that triangle.

Hence the result.