First principles, derivative rules, tangents, stationary points and optimisation formulas for Grade 12 CAPS differential calculus with NSC exam notes.
Differential calculus is worth about 35 marks in NSC Paper 1 and is highly predictable: first principles, rules of differentiation, cubic graph sketching, and rate of change or optimisation.
| Formula | Expression | Note |
|---|---|---|
| Derivative from first principles | f′(x) = lim(h→0) [f(x + h) − f(x)]/h | The limit notation must be written on every line until h is cancelled. |
| Power rule | d/dx [axⁿ] = anxⁿ⁻¹ | Rewrite surds and fractions as powers of x before differentiating. |
| Tangent to a curve | y − y₁ = f′(x₁)(x − x₁) | f′(x₁) is the gradient at the point of contact. |
| Stationary points | f′(x) = 0 | Solve for x, then substitute into f(x) for the y-coordinate. |
| Point of inflection | f″(x) = 0 | For a cubic it is the average of the two stationary point x-values. |
| Rate of change | Rate = f′(t) | Velocity is s′(t) and acceleration is s″(t). |
| Sum and difference rule | d/dx [f(x) ± g(x)] = f′(x) ± g′(x) | Differentiate term by term; expand brackets and simplify fractions first. |
| Derivative of a constant | d/dx [c] = 0 | A constant term disappears when you differentiate. |
| Average gradient | [f(b) − f(a)] ÷ (b − a) | The gradient of the straight line between two points on the curve. |
| Second derivative | f″(x) = d/dx [f′(x)] | f″(x) > 0 means concave up; f″(x) < 0 means concave down. |
Some are printed on the official information sheet, but not all. Treat every formula on this page as examinable and learn it with a worked example so you recognise when to use it.
Differential Calculus is examined in Paper 1 of the NSC Mathematics examination.
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