**Domain of a Function**

The **domain of a function** is the set of all acceptable or allowable input values (also known as x-values) when evaluated into the function. Acceptable x-values are numbers that when evaluated into a function will only yield real numbers.

**Example**: What is the domain of the function y=2x+1?

Can you think of any input value that when evaluated into y=2x+1 will have an output of either an imaginary number or “undefined” answer? The answer is none.

Therefore, the domain of the function y=2x+1 is the set of real numbers. We can also write our answer in set notation.

**Domain**: \left\{ {x|x \in \Re } \right\}

We can read this as “*the set of all x-values such that x is an element of the Real Numbers*“.