由3x＋7y－z＝3 4x＋10y－z＝2 可以求得
x+3y=-1,2x+4y-z=4后面等式减去前面等式得;
x+y-z=5
若x,y,z满足方程租3x＋7y－z＝3 4x＋10y－z＝2 求x＋y－z
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