We know that in the set of nth roots of unity there are exactly $n$ distinct complex numbers: $C_n = \{z \in \mathbb{C} : z^{n} = 1 \} = \{e^{i2k\pi/n}, \; k = 0, 1, ...,n-1 \} $ and they lie on the unit circle. Now collect all roots of unity for every $n \in \mathbb{N}$ and consider the set $C = \{C_n, \; n \in \mathbb{N}\}$.
Is the set $C$ the unit circle, that is $\{C_n, \; n \in \mathbb{N}\} = \{z \in \mathbb{C} : |z| = 1 \}$ ?
Obviously $\{C_n, \; n \in \mathbb{N}\} \subseteq \{z \in \mathbb{C} : |z| = 1 \}$, but I didn't manage to prove the other inclusion (if it is true).