1. “Teach A Level Maths” Vol. 1: AS Core Modules
11:
The Rule for Differentiation
© Christine Crisp

2. Module C1 Module C2 AQA MEI/OCR Edexcel OCR
"Certain images and/or photos on this presentation are the copyrighted property of JupiterImages and are being used with permission under license. These images and/or photos may not be copied or downloaded without permission from JupiterImages"

3. The Gradient of a Straight Line
The gradient of a straight line is given by
where and are points on the line

4. difference in the y-values
e.g. Find the gradient of the line joining the points with coordinates and
Solution:
difference in the y-values x
7 - 1 = 6 x
3 - 1 = 2
difference in the x-values

5. This branch of Mathematics is called Calculus
The gradient of a straight line is given by
We use this idea to get the gradient at a point on a curve
Gradients are important as they measure the rate of change of one variable with another. For the graphs in this section, the gradient measures how y changes with x
This branch of Mathematics is called Calculus

6. The Gradient at a point on a Curve
Definition: The gradient of a point on a curve equals the gradient of the tangent at that point.
e.g.
Tangent at
(2, 4) x 12 3
The gradient of the tangent at (2, 4) is
So, the gradient of the curve at (2, 4) is 4

7. The gradient changes as we move along a curve

14. For the curve we have the following gradients:
Point on the curve
Gradient
At every point, the gradient is twice the x-value

15. For the curve we have the following gradients:
Point on the curve
Gradient
At every point, the gradient is twice the x-value

16. At every point on the gradient is twice the x-value
This rule can be written as
The notation comes from the idea of the gradient of a line being d x y

17. At every point on the gradient is twice the x-value
This rule can be written as
The notation comes from the idea of the gradient of a line being d y d x
is read as “ dy by dx ”
The function giving the gradient of a curve is called the gradient function

18. Other curves and their gradient functions
The rule for the gradient function of a curve of the form is
“power to the front and multiply”
“subtract 1 from the power”
Although this rule won’t be proved, we can illustrate it for by sketching the gradients at points on the curve

19. Gradient of x

20. Gradient of x x

21. Gradient of x x x

22. Gradient of x x x x

23. Gradient of x x x x x

24. Gradient of x x x x x x

25. x x x x x x x
Gradient of

26. x

27. The gradients of the functions and can also be found by the rule but as they represent straight lines we already know their gradients
gradient = 0
gradient = 1

28. Summary of Gradient Functions:

29. The Gradient Function and Gradient at a Point
e.g.1 Find the gradient of the curve at the point (2, 12).
Solution:
At x = 2, the gradient

30. Exercises
1. Find the gradient of the curve at the point where x = - 1
Solution:
At x = - 1, m = -4
2. Find the gradient of the curve at the point At
Solution:

31. The process of finding the gradient function is called differentiation.
The gradient function is called the derivative.
The rule for differentiating can be extended to curves of the form
where a is a constant.

32. More Gradient Functions
e.g. Multiplying by 2 multiplies the gradient by 2
tangent at x = 1
gradient = 3

33. e.g. Multiplying by 2 multiplies the gradient by 2
tangent at x = 1
gradient = 6
tangent at x = 1
gradient = 3

34. Multiplying by a constant, multiplies the gradient by that constant

35. The rule can also be used for sums and differences of terms.
e.g.

36. Using Gradient Functions
e.g. Find the gradient at the point where x = 1 on the curve
Solution:
Differentiating to find the gradient function:
When x = 1, gradient m =

37. SUMMARY
The gradient at a point on a curve is defined as the gradient of the tangent at that point
The function that gives the gradient of a curve at any point is called the gradient function
The process of finding the gradient function is called differentiating
The rule for differentiating terms of the form is
“power to the front and multiply”
“subtract 1 from the power”

38. Exercises
Find the gradients at the given points on the following curves: 1.
at the point
When 2.
at the point
When 3.
at the point
When

39. Exercises
Find the gradients at the given points on the following curves: 4. at
( Multiply out the brackets before using the rule )
When 5. at
(Divide out before using the rule )
When

41. The following slides contain repeats of information on earlier slides, shown without colour, so that they can be printed and photocopied.
For most purposes the slides can be printed as “Handouts” with up to 6 slides per sheet.

42. SUMMARY
The gradient at a point on a curve is defined as the gradient of the tangent at that point
The process of finding the gradient function is called differentiating
The function that gives the gradient of a curve at any point is called the gradient function
The rule for differentiating terms of the form is
“power to the front and multiply”
“subtract 1 from the power”

43. e.g.

44. e.g. Find the gradient at the point where x = 1 on the curve
Solution:
Differentiating to find the gradient function:
When x = 1, gradient m =
Using Gradient Functions