If you want to evaluate a function at a specific point , you'll have to look for on the x axis, and then look vertically for the point on the graph.
The y coordinate of that point is the corresponding y value.
So, for example, if we want , we start from the origin and go up, until we find the point that belongs to the graph. So, we have .
Similarly, for , we start from 2 on the x axis and go up until we meet the point on the graph. So, we have .
For , we start from -8 on the x axis and go up until we meet the point on the graph. So, we have .
For , we start from -6 on the x axis and go down until we meet the point on the graph. So, we have .
The three x-values for which the corresponding y-value is zero are the x-coordinates of the points where the graph crosses the x axis (this means that the y axis is zero). Those three points are