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Syllabus Edition
First teaching 2021
Last exams 2024
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Differentiation (CIE IGCSE Maths: Extended)
Revision Note
Differentiation
What is differentiation?
- Differentiation is part of the branch of mathematics called Calculus
- It is concerned with the rate at which changes takes place – so has lots of real‑world uses:
- The rate at which a car is moving (its speed)
- The rate at which a virus spreads amongst a population
- To begin to understand differentiation you’ll need to understand gradients
How are gradients related to rates of change?
- Gradient generally means steepness.
- For example, the gradient of a road up the side of a hill is important to lorry drivers
On a graph the gradient refers to how steep a line or a curve is
- It is really a way of measuring how fast y changes as x changes
- This may be referred to as the rate at which y
- So gradient describes the rate at which change happens
How do I find the gradient of a curve using its graph?
- For a straight line the gradient is always the same (constant)
- Recall y = mx + c, where m is the gradient
- For a curve the gradient changes as the value of x changes
- At any point on the curve, the gradient of the curve is equal to the gradient of the tangent at that point
- A tangent is a straight line that touches the curve at one point
How do I find the gradient of a curve using algebra?
- This is really where the fun begins!
- Drawing tangents each time you want the gradient of a curve is too much effort
- It would be great if you could do it using algebra instead
- The equation of a curve can be given in the form
- Inputting x-coordinates gives outputs of y-coordinates
- It is possible to create an algebraic function that take inputs of x-coordinates and gives outputs of gradients
- All of this is done without needing to sketch any graphs
- This type of function has a few commonly used names:
- The gradient function
- The derivative
- The derived function
- The way to write this function is
- This is pronounced "dy by dx"
- In function notation, it can be written
- pronounced f-dashed-of-x
- To get from to you need to do an operation called differentiation
- Differentiation turns curve equations into gradient functions
- The main rule for differentiation is shown
- This looks worse than it is!
- For powers of x
STEP 1 Multiply the number in front by the power
STEP 2 Take one off the power (reduce the power by 1)
- 2x6 differentiates to 12x5
- Note the following:
- kx differentiates to k
- so 10x differentiates to 10
- any number on its own differentiates to zero
- so 8 differentiates to 0
- Note the following:
How do I use the gradient function to find gradients of curves?
- Find the x-coordinate of the point on the curve you're interested in
- Use differentiation to find the gradient (derived) function,
- Substitute the x-coordinate into the gradient (derived) function to find the gradient
Examiner Tip
- When differentiating long awkward expressions, write each step out fully and simplify the numbers after
- Don't forget to write the left-hand sides of y = .... and = ... to avoid mixing up the curve equation with the gradient function
Worked example
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