Let f : R → R given by f (x) = x³.

Suppose f(x) = f(y), where x, y ϵ R.

⇒ x³ = y³ …(1)

Now, we need to show that x = y.

Suppose x ≠ y, their cubes will also not be equal.

⇒ x³ ≠ y³

However, this will be contraction to (1).

Thus, x = y

Therefore, f is injective.