Final answer:
Among the given options, b. f(x) = 3^x represents an exponential function because it is in the form f(x) = a^x where 'a' is a constant and 'x' is the exponent.
Step-by-step explanation:
The question is asking to identify which function among the given options represents an exponential function. An exponential function is usually of the form f(x) = a^x, where 'a' is a constant, and 'x' is the exponent.
Looking at the given options, b. f(x) = 3^x is the function that fits this form, so it is the exponential function. Option a. represents a quadratic function because of the x^2 term. Option c. represents a power equation in two variables x and y, which is not an exponential function in terms of one variable x. Therefore, the correct answer is b. f(x) = 3^x.