The expressions f(x) = x^2 + 2x and g(x) = 2x + 1 are mathematical functions, where f(x) and g(x) are mapping every element x in the domain to a unique output value in the codomain.
The first function f(x) describes a parabolic function with a leading coefficient of x^2, while the second function g(x) is a linear function with a slope of 2 and y-intercept of 1.