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Finding the gradient of a straight-line graph
It is often useful or necessary to find out what the gradient of a graph is. For a straight-line graph, pick two points on the graph. The gradient of the line = (change in y-coordinate)/(change in x-coordinate) .



In this graph, the gradient = (change in y-coordinate)/(change in x-coordinate) = (8-6)/(10-6) = 2/4 = 1/2
We can of course use this to find the equation of the line. Since the line crosses the y-axis when y = 2, the equation of this graph is y = ½x + 2 .


Finding the gradient of a curve
To find the gradient of a curve, you must draw an accurate sketch of the curve. At the point where you need to know the gradient, draw a tangent to the curve. A tangent is a straight line which touches the curve at one point only. You then find the gradient of this tangent.

Find the gradient of the curve y = x² at the point (3, 9).




Note: this method only gives an approximate answer. The better your graph is, the closer your answer will be to the correct answer. If your graph is perfect, you should get an answer of 6 for the above question.

 © Matthew Pinkney