Chapter 7 - Similarity - 7-4 Similarity in Right Triangles - Practice and Problem-Solving Exercises - Page 465: 11

$\triangle MON$ ~ $\triangle MPO$ ~ $\triangle OPN$

In a right triangle that is cut by its altitude, the three triangles formed are similar to one another. We just need to make sure that we have the correct corresponding vertices: $\triangle MON$ ~ $\triangle MPO$ ~ $\triangle OPN$