先化简在求值：（x的平方-xy分之x的平方-2xy+y的平方）÷（y分之x-x分之y）,其中x=3-根号3,y=根号3

原式=[(x²-2xy+y²)/(x²-xy)]÷(x/y-y/x)={(x-y)²/[x(x-y)]}÷[(x²-y²)/(xy)]=[(x-y)/x]×{xy/[(x+y)(x-y)]=y/(x+y)=(√3)/(3-√3+√3)=(√3)/3