f(x) = x³ + 4x - 1
The domain of a function is the range of its inverse and the range of a function is the domain of its inverse. Thus, to find f⁻¹(x), we put the given value of x into f(x) of the original equation.
a) -1 = x³ + 4x - 1
x = 0
f⁻¹(-1) = 0
b) 4 = x³ + 4x - 1
x = 0.25
f⁻¹(4) = 0.25
