A student tries to differentiate f(x)=kx3f(x)=kx^3f(x)=kx3 from first principles, where k k\,k is a constant. The student writes
f(x+h)−f(x)h=k(x3+3x2h+h3)−kx3h\dfrac{f(x+h)-f(x)}{h}=\dfrac{k(x^3+3x^2h+h^3)-kx^3}{h}hf(x+h)−f(x)=hk(x3+3x2h+h3)−kx3.
Identify the error and complete a correct first-principles derivation of f′(x)f'(x)f′(x).
8 exam-style questions on OCR A Level Maths 1.7.7 Differentiation from first principles for powers of x. Each one has a worked solution and a mark scheme showing where the marks go.