Differentiation: find gradients of curves and stationary points. The only IGCSE that includes calculus β A* topic.
What youβll learn
Mapped to the Pearson Edexcel IGCSE 4MA1 syllabus (2026 onwards).
3.7 β Differentiate polynomial functions.
3.7 β Find gradient at a specific point.
3.7 β Find stationary points and determine their nature.
The power rule
Multiply by power, reduce by 1.
Power rule:dxdβ(xn)=nxnβ1.
Examples:
y
dxdyβ
x2
2x
x3
3x2
x4
4x3
x
1 (since x=x1, 1β x0=1)
1/x=xβ1
βxβ2=β1/x2
xβ=x1/2
21βxβ1/2
5 (constant)
0
Constants multiply through:
dxdβ(kf(x))=kβ dxdβ(f(x)).
So dxdβ(3x4)=3β 4x3=12x3.
Sums and differences:
dxdβ(f+g)=dxdfβ+dxdgβ.
So dxdβ(x3β2x+5)=3x2β2+0=3x2β2.
Worked qualitative. Why does the constant disappear?
Derivatives measure RATE OF CHANGE.
A constant doesn't change.
So its rate of change is 0.
Edexcel tip. Show every term's derivative explicitly. Mark schemes credit each term separately.
Power rule: nxnβ1.
Multiply, then reduce.
Constants β 0.
Sum: differentiate term by term.
Gradient at a specific point
Differentiate, then substitute the x-value.
Method:
Differentiate y to get dxdyβ.
Substitute the x-value of the point.
The result is the gradient at that point.
Example.y=x3β2x+5. Find gradient at x=2.
dxdyβ=3x2β2.
At x=2: 3(4)β2=10.
Gradient = 10.
The value of dy/dx at x = 3 is the gradient of the tangent touching the curve there.
Tangent line at a point.
If you have the point (a,b) and gradient m at that point:
Equation of tangent: yβb=m(xβa).
Example. Tangent to y=x2 at (3,9).
Gradient: dxdyβ=2x=6 at x=3.
Equation: yβ9=6(xβ3)βy=6xβ9.
Worked qualitative. What's the gradient of y=x2 at the origin?
dxdyβ=2x.
At x=0: gradient = 0.
The curve has a horizontal tangent at the vertex.
Edexcel tip. Show the differentiation step AND the substitution step separately. Mark schemes credit both.
Differentiate, then substitute.
Gradient = dxdyβ at x.
Tangent: yβy1β=m(xβx1β).
Always show both steps.
Stationary points
Set dxdyβ=0, solve. Find y. Determine nature.
Stationary point: where dxdyβ=0. The curve has zero gradient (horizontal tangent).
Could be:
MINIMUM (low point, curve goes up either side).
MAXIMUM (high point, curve goes down either side).
POINT OF INFLECTION (rare at IGCSE).
Stationary points have a horizontal tangent; the second derivative tells you which is which.
Method:
Differentiate y to get dxdyβ.
Set dxdyβ=0. Solve for x.
Substitute back into ORIGINAL y equation to find y.
Determine nature.
Determining nature.
Method A: Second derivative test.
If dx2d2yβ>0 at the point: MINIMUM.
If dx2d2yβ<0: MAXIMUM.
If =0: inconclusive (rare at IGCSE).
Method B: Sign change test.
Test dxdyβ either side of the point.
β then +: MINIMUM.
+ then β: MAXIMUM.
Same sign: point of inflection.
Worked example.y=x3β3x2β9x+5.
dxdyβ=3x2β6xβ9.
Set =0: x2β2xβ3=0. Factor: (xβ3)(x+1)=0. x=3 or x=β1.
Find y:
x=3: 27β27β27+5=β22. Point: (3,β22).
x=β1: β1β3+9+5=10. Point: (β1,10).
Second derivative: dx2d2yβ=6xβ6.
At x=3: 12>0 β MIN.
At x=β1: β12<0 β MAX.
So: minimum at (3,β22), maximum at (β1,10).
Worked qualitative. Why does the second derivative tell us min vs max?
Second derivative = rate of change of GRADIENT.
>0: gradient is INCREASING (going from β to +) β curve curves UP β MIN.
<0: gradient is DECREASING (+ to β) β curve curves DOWN β MAX.
Edexcel tip. Always determine NATURE β Edexcel asks for it. Use second derivative or sign change test.
Set dxdyβ=0.
Solve for x.
Find y from original.
Determine nature: dx2d2yβ.
>0 min, <0 max.
How itβs examined
Calculus appears Higher Tier (4-7 marks). Differentiation, gradient at a point, stationary points, sometimes tangents. Examiner reports flag (1) not multiplying by the power, (2) skipping nature determination, (3) stating only x for stationary points.
Differentiate each term separately. Constants (β2 here) differentiate to 0.
3Find gradient at a specific point
Higherβ’ gradient, differentiation
βΌ
Question
y=x3β2x+5. Find the gradient at the point where x=2.
Step-by-step solution
Step 1
Differentiate: dxdyβ=3x2β2.
Step 2
Substitute x=2: 3(4)β2=10.
Answer
Gradient = 10
4Find stationary points
Higherβ’ Adapted from 4MA1/1H Jan 2024 Q18β’ stationary points
βΌ
Question
Find the stationary points of y=x3β3x2β9x+5 and determine their nature.
Step-by-step solution
Step 1
Differentiate: dxdyβ=3x2β6xβ9.
Step 2
Set dxdyβ=0: 3x2β6xβ9=0βx2β2xβ3=0.
Step 3
Factor: (xβ3)(x+1)=0. So x=3 or x=β1.
Step 4
Find y: at x=3, y=27β27β27+5=β22. At x=β1, y=β1β3+9+5=10.
Step 5
Nature: test second derivative or values either side. dx2d2yβ=6xβ6. At x=3: 12>0 β minimum. At x=β1: β12<0 β maximum.
Answer
(3,β22) minimum; (β1,10) maximum
Examiner tip
Stationary point: where dxdyβ=0. Use second derivative test for nature: >0 β min, <0 β max.
Key Formulae β Calculus
The formulae you need to memorise for calculus on the Pearson Edexcel IGCSE 4MA1 paper, with every variable defined in plain English and a note on when to use it.
Power rule for differentiation
dxdβ(xn)=nxnβ1
n
any real number
When to use
Differentiating a power of x. Multiply by the power, then reduce by 1.
Example
dxdβ(x4)=4x3. dxdβ(3x2)=6x.
Key Definitions and Keywords β Calculus
Definitions to memorise and the exact keywords mark schemes credit for calculus answers β sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE 4MA1 sitting.
Derivative
Examiner keyword
dxdyβ β the rate of change of y with respect to x. Gradient of the curve.
Example
y=x2 has dxdyβ=2x.
Stationary point
Examiner keyword
A point where dxdyβ=0. Could be a maximum, minimum, or point of inflection.
Maximum / minimum (turning point)
Stationary points where the function reaches a local high or low. Determined by second derivative or sign change.
Common Mistakes and Misconceptions β Calculus
The traps other students keep falling into on calculus questions β taken from recent Pearson Edexcel IGCSE 4MA1 examiner reports and mark schemes β and how to avoid them.
βNot multiplying by the power
4MA1/2H May/Jun 2024 β examiner report Q21
βΌ
Why it happens
Forgetting first half of the rule.
How to avoid it
Power rule: BRING DOWN the power, then REDUCE by 1. x4β4x3, NOT just x3.
βNot differentiating constants to zero
βΌ
Why it happens
Treating constants like variables.
How to avoid it
Constants: dxdβ(c)=0. They DISAPPEAR. 5β0, β7β0.
βStating only x for stationary point, not (x,y)
4MA1/1H Jan 2024 β examiner report Q18
βΌ
Why it happens
Solving dy/dx=0 gives x.
How to avoid it
STATIONARY POINTS are POINTS. Always state as (x,y). Substitute x back into ORIGINAL equation to find y.
Practice questions
Exam-style questions with step-by-step worked solutions. Try one before checking the method.
Past paper style quiz
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4. Exam Quiz
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Video lesson
Short walkthrough of the concepts students most often get stuck on.
Calculus β frequently asked questions
The things students keep getting wrong in this sub-topic, answered.