1 problem

Let $\mathcal{S}_{3,1}=\{\bm{x}\in\mathbb{R}^3:x_1^2+x_2^2+x_3^2=1\}$, and let $E_{2,2}(A)$ denote the number of quadruples $(\bm{x}_1,\bm{x}_2,\bm{x}_3,\bm{x}_4)\in A^4$ satisfyin…