A graph is a picture that shows all the values of the variables that make the equation or inequality true. Usually this is easy to make when there are only one or two variables. The graph is often a line, and if the line does not bend or go straight up-and-down it can be described by the basic formula y = mx + b. The variable "b" is the y-intercept of the graph (where the line crosses the vertical axis) and "m" is the slope or steepness of the line. This formula applies to the coordinates of a graph, where each point on the line is written (x, y). 