Plotting Graphs

Plotting coordinates

Basics to remember:

The x axis is horizontal.

The y axis is vertical.

Plot x and then y, remember like going along the corridor and up the stairs it still works! Though when you have four quadrants sometimes you will go downstairs to the basement or out to the backyard.

Plotting Graphs, figure 1

Drawing straight line graphs

To draw straight lines on graphs you will need an equation. For example y=2. In this case all the value of y on the graph will be equal to 2. This means that the graph will cross the y axis at 2, a you can see below:

Plotting Graphs, figure 1

For graphs that are x=a for example x=3 ,the x value on the graph will ALWAYS be 3, no matter what the y value is. Therefore it will create a vertical line that goes through x=3

Plotting Graphs, figure 2

For lines that have more complicated equations such as y=3x+1 we need to work out some x and y coordinates. The best way to do this is to create a table of values. You can choose to make x whatever you want, so make sure you choose values that enable you to draw a clear graph. I would recommend creating a table like this:

Plotting Graphs, figure 3

If it is a straight line graph you should see a pattern forming in the values of y, as you can see in the table the values of y increase each time by 3. Now that you have your coordinates you need to plot them and carefully draw a straight line through the points with a ruler. If your points do not create a straight line check your working and check that the equation you have is not a quadratic. If it has an x2 or any other index number it will not be a linear graph.

Plotting Graphs, figure 4

Make sure you draw your line through the points on your graph.

Draw a 10 by -10 graph and plot the points ( 0,-1) (0,1) and (0,1), join the dots, what shape do you get?