Question 21
For real numbers $x_1, x_2, \dots, x_{60} \in [-1, 1]$, find the maximum of
$$
\sum_{i=1}^{60} x_i^2 (x_{i+1} - x_{i-1}),
$$
where $x_0 = x_{60}, x_{61} = x_1$.
$$
\sum_{i=1}^{60} x_i^2 (x_{i+1} - x_{i-1}),
$$
where $x_0 = x_{60}, x_{61} = x_1$.