Final answer:
A line graph is used to represent the relationship between two changing variables and is particularly useful for illustrating time series data, like shifts in the unemployment rate over time. Series of related values on the graph are differentiated by unique colors or patterns.
Step-by-step explanation:
The question relates to the graphical representation of data in a line graph. A line graph is valuable for showcasing the relationship between two variables, especially when both variables change. For instance, a time series graph can effectively illustrate how data points change over time, such as the unemployment rate. In the graphing context, series of related values are typically represented by unique colors to distinguish between different data sets or patterns.
When the data depicts a direct relationship between two variables, the graph will show this as a straight line. Each axis of the graph holds significant meaning, where the x-axis usually represents individual data values and the y-axis shows frequency or another variable.