# Function notation

**Functions**

A** function** is a rule that maps the input (*x*) onto the output (*y*), in both cases, *x* and *y* are numbers. For example:

When *x² *is* y,* the **functional notation** is:

ƒ(*x*) = *x*² (or the *f* of *x* equals *x* squared)

Also, the function of *f* can act on any number, term or expression that is a bracket. Therefore:

*f*(2) = 2² = 4

*f*(-*x*) = (-*x*)² = *x*