A linear relationship (or linear association) is a statistical term used to describe the directly proportional relationship between a variable and a constant.

Learn and revise how to solve quadratic equations by factorising, completing the square and using the quadratic formula with Bitesize GCSE Maths Edexcel.

Revise how to plot a linear equation graph. Learn how to read x and y coordinates from a graph in this BBC Bitesize maths KS3 guide.

I displayed these d values on the graph for you. Notice that they are the vertical distance from the real data points to the fitting linear function. Why this way?