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7x-12y=31(1) 12x-7y=26(2) (2)-(1)得5x+5y=-5,即x+y=-1(3) (1)+(2)得19x-19y=57,即x-y=3(4) (3)+(4)得:2x=2,即x=1 (3)-(4)得:2y=-4,即y=-2
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