A straight line graph with two variables is represented by an equation such as 𝑦 = 3𝑥 – 7. The equation shows the link between the 𝑥 and 𝑦-coordinates.

To be parallel, two lines must have the same gradient. The gradient of y = 3 x + 7 is 3. Any line with a gradient of 3 will be parallel to y = 3 x + 7. Two examples are y = 3 x 2 and y = 3 x + 11.6.

For example, you could look at the daily sales of ice cream and the daily high temperature as the two variables at play in a graph and find a crude linear relationship between the two.