functional equations, simultaneous functional equations.
[STEP III 2016 Question 8 (Pure Mathematics)]
Logarithm, exponential and trigonometric functions, Maclaurin series.
[STEP III 2006 Question 4 (Pure)]
Underground Mathematics: Selected worked STEP questions
STEP Question database
University of Cambridge Mathematics Faculty: What do we look for?
University of Cambridge Mathematics Faculty: Information about STEP
University of Cambridge Admissions Office: Undergraduate course information for Mathematics
Stephen Siklos' "Advanced Problems in Mathematics" book (external link)
MEI: Worked solutions to STEP questions (external link)
OCR: Exam board information about STEP (external link)
AMSP (Advanced Maths Support programme): Support for University Admission Tests (external link)