Final answer:
The expression Tr^3 is a monomial because it consists of a single term, made up of a constant and a variable to a power. Its degree is 3, which corresponds to the exponent of the variable r.
Step-by-step explanation:
The expression Tr^3 is considered a monomial because it is a single term consisting of a product of a constant (T) and a variable (r) raised to a power. A monomial is an algebraic expression with only one term. In the given expression, the variable r is raised to the third power, thus the operation involved is the cubing of exponentials. When r is cubed (r^3), the exponent of the variable is simply multiplied by 3 as a part of the exponentiation process.
The degree of a monomial is found by summing the exponents of all the variables in the term. In this case, since r is the only variable and its exponent is 3, the degree of the monomial Tr^3 is 3.