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How do I prove that this functions is injective?

a.) f : x --> x³ + x x ∈R

f(a) = a³ + a, f(b) = b³ + b

f(a) = f(b) => a³ + a = b³ + b => a³ = b³

=> a = b

therefore f is one-to-one

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# Proof of injective function

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