Calculus
We introduce the concept of the derivative from first principles and apply differentiation rules to polynomial functions. We find equations of tangents and normals.
6.1 Differentiation — Rules & Tangent Lines
- Determine the derivative from first principles: $f'(x)=\lim_{h\to0}\frac{f(x+h)-f(x)}{h}$
- Apply differentiation rules: constant, power, sum/difference
- Find equations of tangent and normal lines to curves
Real-World Connection
The speedometer in a car measures the DERIVATIVE of position with respect to time — how quickly position changes each instant. The derivative is the mathematical formalisation of 'instantaneous rate of change', which appears everywhere from physics to economics.
Definition
Derivative (First Principles)
The derivative of at is the limiting value of the average rate of change as the interval shrinks to zero.
Power Rule
Works for any real $n$
Constant Rule
Derivative of any constant is 0
Sum/Difference Rule
Differentiate term by term
Property / Rule
Tangent and Normal Lines
The gradient of the tangent to at is . The normal is perpendicular to the tangent, so its gradient is .
🚨 Common Mistake
Before differentiating, SIMPLIFY the expression. should be simplified to first. The power rule applies ONLY to individual power terms.
Worked Example
Derivative from first principles
Problem
Worked Example
Tangent line to a curve
Problem
CAPS Cognitive Level Distribution