①2x+5y-13z=1000②3x-9y+3z=0③5x-6y-8z=6000将②式除以3得：④x-3y+z=0①-2×④得：⑤11y-15z=1000③-5×④得：⑥9y-13z=60009×⑤-11×⑥得：8z=-57000,即⑦z=-7125将⑦代入⑥得：⑧y=-9625将⑦⑧代入④得：x=-21...