Ta có:
\begin{array}{l} {x_5} = \left( {{x_1} + {x_2} + {x_3} + {x_4} + {x_5}} \right) - \left( {{x_1} + {x_2}} \right) - \left( {{x_3} + {x_4}} \right)\\ \,\,\,\,\, = 0 - 2 - 2 = - 4\\ {x_4} = \left( {{x_5} + {x_4}} \right) - {x_5} = 2 - \left( { - 4} \right) = 6\\ {x_3} = \left( {{x_3} + {x_4}} \right) - {x_4} = 2 - 6 = - 4 \end{array}