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Year 9 · Functions & Graphs

Function notation

Function notation f(x) means "the rule applied to x". f(3) is the rule with 3 put in.

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How to do it

  1. Substitute the number for every x.
  2. Composite f(g(x)): work out g first, then put the result into f.
  3. Inverse: swap x and y, then make y the subject.

Worked example

f(x) = x² + 3x − 7. Find f(-2).
Substitute x = -2: (-2)² + 3(-2) − 7 = 4 + -6 − 7 = -9.
Answer: -9

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Inside brackets first for composite functions.

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