We use a graph to study the relationship between two or more measured quantities. Very often we study the relation between a dependent variable and an independent variable. For example the relation between the position of a moving object and time can be written as:

y = 2 t + 5

Here y is the position of the object which depends on the time t. Therefore, t is the independent variable and y is the dependent variable.

We graph the independent variable along the x axis and the dependent variable along the y axis.

Question: y = mx + b is a linear relation between x and y. What does this mean? What is the shape of the graph of y against x? What does m and b represent in this relation?

Question: What is the shape of the graph of y against t of y = 2t + 5? What do the numbers 2 and 5 represent?