Which of the following represents a cubic function?

A cubic function is defined as a polynomial function of degree three, meaning that the highest power of the variable (x) is three. The general form of a cubic function can be expressed as (f(x) = ax^3 + bx^2 + cx + d), where (a), (b), (c), and (d) are constants and (a \neq 0). This structure allows the function to exhibit the distinct properties and behaviors associated with cubic equations, such as having up to three real roots and the capability to change direction at most twice.

In contrast, the other options do not represent cubic functions. The second option describes a polynomial of degree four, which would not qualify as a cubic function. The third and fourth options present formulas related to geometry, specifically calculating areas, rather than defining algebraic functions. Thus, the only correct choice that accurately mirrors the characteristics of a cubic function is the first one.