Determining if a Relation is a Function

In an ordered pair $(a,b),$ $a$ represents the input value and $b$ the output value. Since $x\text{-}$values are the inputs and $y\text{-}$values are the outputs, we can write five ordered pairs. $$\begin{array}{c}(1,75),(2,100),(3,125),(4,150),(5,175)\end{array}$$

Let's now plot the ordered pairs. Recall that the first coordinate corresponds to the horizontal axis, and the second coordinate to the vertical axis.