We have seen that if y is a function of x, then for each given value of x, we can determine uniquely the value of y as per the functional relationship. For some functions, it is possible to express x in terms of y so that, given the value of y, the value of x can be uniquely determined. The function that expresses the variable x in terms of the variable y is called the inverse function and is denoted by x = f^{-1} (y).
Example
y = f(x) = 5x + 3
Solving x in terms of y,
x