7x-12y=67,(1)式12x-7y=47, (2)式(1)+(2), 19x-19y=114, x-y=6 (3)(2)-(1), 5x+5y=-20, x+y=-4(4)(3)+(4), 2x=2, x=1(4)-(3), 2y=-10, y=-5m比n的一半大1, m1=1+(n/2), 2m-2=nx=2, y=-1代入3x-2ny=m-n, 6+2n=m-n, m=3n+6 代入上式2(3n+6)-2=n, 6n+12-2=n, 5n=-10, n=-2m=3n+6=-6+6=0m=0, n=-2
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