(x+y)/(xy)=1/(x-y)(x²-y²)/(xy)=1两边平方：(x^4-2x²y²+y^4)/(x²y²)=1(x^4+2x²y²+y^4)/(x²y²)=5[(x²+y²)/(xy)]²=5∴(x²+y²)/(xy)=±...