Instructional video. Simple. So if we look here, they've graphed the point--it looks like negative 1, 3, so that's the point negative 1, 3. The easiest way to make a graph is to begin by making a table containing inputs and their corresponding outputs. So in order for the points to represent a function, for every input into our function, we can only get one value. If each x value has a unique y value, then the graph represents a function. If any vertical line intersects the graph more than once, then the graph does not represent a function. THE VERTICAL LINE TEST A graph (or set of points) in the plane is a FUNCTION if no vertical line contains more than one of its points. In algebra, there are 3 basic types of graphs you'll see most often: linear, quadratic, and exponential. In this lesson you will learn how to tell if a line on a graph represents a function by mapping inputs to outputs. For example, consider the function y = 2x + 1. We can easily determine whether or not an equation represents a function by performing the vertical line test on its graph. All points must lie along the curve for it to be a function. Check out this tutorial and learn how to determine is a graph represents a linear, quadratic, or exponential function! We can also represent functions using graphs by plotting all the ordered pairs of a function on a coordinate axis. Graphs come in all sorts of shapes and sizes. At the line which crosses the x axis at 3, y will = 6. Put x into the equation, say 3, so y = 2*3 = 6. This test is called the vertical line test. vertical line test to determine if a graph represents a function Graphs. which graphs are functions? Look at where the graph crosses the X-axis at the point [math]x=0[/math]. The [math]cos(0) = 1 [/math]and [math]sin(0)=0[/math]. 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