x+y分之x-y=2 求x+y分之3x-3y 减x-y分之2(x+y)的值 x+y分之x-y=2 x-y=2(x+y) (x+y)分之(3x-3y)-(x-y)分之2(x+y)的值 x+y分之3x-3y =(x+y)分之3(x-y) =(x+y)分之6(x-y) =6 -x-y分之2(x+y) =-(x+y)分之2(x+y) =-2所以(...