二分之(x+y)+三分之(x-y)=13两边同时乘以6得:3(x+y)+2(x-y)=78=>y=78-5x .三分之x+y-四分之x-y=3两边同时乘以12得4(x+y)3(x-y)=18得y=18-7x,所以18-7x=78-5x得x=-30 y=228~