If triangle mnp is congruent to triangle pnm, classifytriangle
mnp by its sides.

MNP is a Congruent Triangle according to Side-Side-Side Congruence.

Step-by-step explanation:

Whenever we talk about Euclidean Geometry and Congruence of Triangles. We are taking into account that in any given plane, three given points, in this case, M, N, and P is and its segments between two points make up a Triangle.

In this case MNP and an identical one and PNM

To be called congruent, it's necessary to have the same length each side and when it comes to angles, congruent angles have the same measure.

A postulate, cannot be proven since it's self-evident. And there's one that fits for this case which says

"Every SSS (Side-Side-Side) correspondence is a congruence"

So this is why we can classify MNP as Side-Side-Side congruence since its segments are the same size MN, NP, and MP for both of them. The order of the letters does not matter.