x+y/2+x-y/3=7 ① x+y/3-x-y/4=-1 ② 设x+y=m x-y=n 则方程组变为 m/2+n/3=7 3m+2n=42 (1) m/3-n/4=-1 4m-3n=-12 (2) (1)*3+(2)*2 17m=102 m=6 代入(1) n=12 于是x+y=6 (3) x-y=12 (4) (3)+(4) 2x=18 x=9 代入(3) y=-3
