2 Para un entero $n\ge 2$ halle todos los $a_1,a_2,\cdots ,a_n, b_1,b_2,\cdots , b_n$ tales que (a) $0\le a_1\le a_2\le \cdots \le a_n\le 1\le b_1\le b_2\le \cdots \le b_n;$ (b) $\sum_{k=1}^n (a_k+b_k)=2n;$ (c) $\sum_{k=1}^n (a_k^2+b_k^2)=n^2+3n.$