Inverse operation

In mathematics, an inverse operation reverses what another operation did. 

 Definitions 
We say f is a function if there is only one f value for every x value. In a similar way, the inverse is only a function if there is only one x for every f value. In that case we say that f is invertible. 

 Examples 

 Squares and Square Roots 
If the variable x is any number then x times x is written as x². This is called the square of x. The square root of x², written as  is the operator that reverses the operation x times x. Because x times x and -x times -x both give the same answer, there are two possible answers to the question "What is the square root of x²?" This means that x² is not invertible.