Final answer:
None of the given options are mathematically equivalent to the equation S = r^2n.
Step-by-step explanation:
The given equation S = r^2n represents an expression where S is equal to the area of a cross-section of an object, r is the radius of the object, and n is a constant or exponent.
Looking at the options, none of them are mathematically equivalent to the given equation. Option A and B are unrelated, Option C is unrelated as it has different variables, and Option D has a different expression entirely. Therefore, none of the options are equivalent to the given equation S = r^2n.