已知x²-xy-y²=0,且x≠0,y≠0.求代数式（x²-2xy-5y²）/（x²+2xy+5y²）的值

已知x²-xy-y²=0,且x≠0,y≠0.求代数式（x²-2xy-5y²）/（x²+2xy+5y²）的值

(x+y)(x²-xy-y²)=0, => x^3-y^3=0, x=y
（x²-2xy-5y²）/（x²+2xy+5y²)=-6/8=-3/4=-0.75