ACT Preparation / Unit 10 ACT 0924 short lesson, about 20 seconds
Inverse Functions
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The idea
The inverse of a one-to-one function f, written f⁻¹, undoes f: if f(a) = b, then f⁻¹(b) = a, and f⁻¹(f(x)) = x.
In practice
f(x) = 2x + 3 sends 4 to 11; its inverse sends 11 back to 4.
Where people slip
f⁻¹(x) is not 1/f(x); the −1 marks the inverse, not a reciprocal.
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