I recently learned of the terms AP and GP, which mean Algebraic Progression and Geometric Progression, respectively. As I understand it: given a constant, $k$, and the sides of a triangle, $a$, $b$, and $c$,
the triangle is in AP if $$\left\{\begin{matrix}a+k=b\\b+k=c\end{matrix}\right\},$$
and the triangle is in GP if $$\left\{\begin{matrix}ka=b\\kb=c\end{matrix}\right\}$$
I am trying to understand why we prove that a triangle is in AP or GP.
Do the definitions of AP triangles and GP triangles allow us to prove anything non-trivial about the triangles?