Day 2 · One-One and Onto Functions

A one-one (injective) function is one where different inputs always give different outputs — no two domain elements map to the same value.

An onto (surjective) function is one where every element in the codomain has at least one pre-image — the range equals the codomain.

f(x) = x³ from R to R is both one-one and onto, but f(x) = x² from R to R is not one-one, because f(2) = f(-2) = 4.

Activity: Consider whether f(x) = x + 1 from R to R is a one-one function.