 So far we know that to the important parts of a line graph are the x-intercept, y-intercept and the gradient, or slope.

X - intercept Y-intercept Gradient or slope

 y = mx + c is the basic rule for any line graph.  The letter m and x represent different aspects that can be read of a graph

 C is the easier of the two letters to work out from a graph.  It is simply the value of the y-intercept. So the point where the graph crosses the y-aixs is the value of c.

 Find the value of ‘c’ in the following graphs X Y

 The letter ‘m’ in y =mx + c represents the gradient or slope of a graph.  M is found by working out the rise of a graph and then the run, or movement across, of the graph.  M = rise run

Choose a spot on the graph that sits on a value on a y value 2. State the y-value of this point Y = 0 3. Choose another point on the graph that sits on a y value 4. State the y-value of this point. Y = 2 5. Find the difference between these two points, the rise Rise = 2 – 0 Rise = 2

IMPORTANT: If a graph slants downwards from left to right, then it is actually a drop rather than a rise and you must put a negative (-) in front.

Find the points that you would use for the rise 2. Find the x- value of the first point 3. Find the x- value of the second point 4. Find the total movement across, the run X = -2 X = 0 Run = -2 to 0 So total movement across is 2 Run = 2

 Now that you know how to find the rise and the run separately, you need to put the two of them together to find the value of m.

Find the rise 2. Find the run 3. Solve rise run Rise = 0 to 3 Rise = 3 Run = -1 to 0 Run = 1 m = rise run m = 3 1 m = 3

Find the value for c 2.Find the value for m 3.Put the found values into the equation What is the y-intercept? C = -3 What is the gradient? m = 3 2 Put this into the rule… y = 3x – 3 2