Existence and Uniqueness of Positive Root of Positive Real Number

Theorem
Let $$x \in \mathbb{R}$$ be a real number such that $$x \ge 0$$.

Let $$m \in \mathbb{Z}$$ be an integer.

Then there always exists a unique $$y \in \mathbb{R}: y \ge 0$$ such that $$y^m = x$$.