The symbolic idea here, is that the vertical side represents one aspect, the horizontal side another aspect and the hypotenuse is offspring of the combining sides. The combination of one and another produces a new form of being altogether (a child, as it were).
This, among other complexities is where the triangle symbol meaning of creation/creativity is stemmed. Each side and corner sings out a melody, and their combination in form creates a marvelous harmonic orchestration.