3（x+y)-4(x-y)=4 (a) x+y/2+x-y/6=1 (b) 由a得：3x+3y-4x+4y=4 7y-x=4 x=7y-4 (c) 将c带入b得 7y-4+y/2+7y-4-y/6=1 14y-8+y/3=1 y=27/43 可得x=17/43
