The general equation for a straight line is given by y = mx + c.
"m" is the gradient and
"c" is the value of the intercept the line makes with the vertical axis.
Let's start with an example y = (5/4) x + 2 .
The intercept that the straight line will make with the vertical axis is "+2" indicated by the red dot in Diagram 1.
Next, we noticed that the gradient is m = (5/4). This meant that the vertical change is 5 units upwards (positive number) for a horizontal change of 4 units in the positive (right-going) direction. Let's find the other spot on the straight line. (Diagram 2)
The other spot is identified after moving from the first red dot 5 units up and 4 units right. The unit movement is based on the gradient (m = 5/4) set in the equation.
Note: To draw a straight line graph, we only need 2 points.
With the 2 points identified, we are now ready to draw the line connecting the 2 red points.
To summarise, we just need to follow 3 steps:
- Identify the intercept (c) from the equation and indicate it on the vertical axis
- Find the other point using the gradient (m) as a guide with the point in step 1 as start reference
- Connect the 2 points identified to obtain the straight line graph
This is as simple as A B C !
Another example: y = -2 x + 7.
The y-intercept is "+7" and the gradient is "-2", meaning, a drop of 2 units for 1 unit movement to the right. The graph is shown below (Diagram 4).