Školjka

%V0 Let $n \in \mathbb{Z}^+$ and let $a, b \in \mathbb{R}.$ Determine the range of $x_0$ for which $$\sum^n_{i=0} x_i = a \text{ and } \sum^n_{i=0} x^2_i = b,$$ where $x_0, x_1, \ldots , x_n$ are real variables.