What is NOT considered a branch of mathematics?

The correct answer is that the term "hypotenuse" does not represent a branch of mathematics. Instead, it refers to a specific side of a right triangle, which is the longest side opposite the right angle. This term is more aligned with geometric concepts rather than an entire field of study.

On the other hand, "triangle" represents a shape studied within geometry, which is indeed a branch of mathematics, albeit it's a more specific concept rather than a complete field. Meanwhile, both "Linear Algebra" and "Real Analysis" are established branches of mathematics focusing on various advanced topics. Linear Algebra deals with vector spaces and linear mappings between these spaces, while Real Analysis involves the study of real numbers and real-valued sequences and functions.