Final answer:
The proof of Theorem 2.15 about left multiplication transformation typically falls under algebra, which includes operations on algebraic expressions and matrices, rather than geometry, calculus, or number theory.
Step-by-step explanation:
The proof of Theorem 2.15 regarding left multiplication transformation most likely involves concepts in algebra, since it deals with operations on algebraic expressions and matrices. In algebra, we often encounter situations where we need to manipulate equations and invert functions to solve for a particular variable.
For example, to find the side length of a triangle using the Pythagorean Theorem, we would isolate the variable by undoing the square, which involves algebraic operations. Transformations such as left multiplication by a matrix also fit within the realm of algebra, especially linear algebra, which is a field that deals extensively with matrices and vector spaces.
This question does not seem to directly involve geometry, calculus, or number theory; however, broader contexts in which such theorems are applied may touch upon concepts from these other areas of mathematics.