What is it
A function is a rule that takes an input and produces exactly one output — KS3 introduces function machines and simple notation like f(x), building the idea that maths can describe relationships, not just calculations.
Why it matters
Function notation appears throughout GCSE and A-Level maths, from simple substitution to composite and inverse functions — getting comfortable with the idea of a function as a rule (not just a formula) pays off for years.
Exam tip
Think of f(x) as 'do this to x' rather than a mysterious symbol — reading it out loud as an instruction makes evaluating functions far less intimidating.
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