已知y/x-x/y=5,求分式3x^2+xy-3y^2/2x^2-xy-2y^2

y/x-x/y=5
(y²-x²)/(xy)=5 /等式左边通分
x²-y²=-5xy
(3x²+xy-3y²)/(2x²-xy-2y²)
=[3(x²-y²)+xy]/[2(x²-y²)-xy]
=[3·(-5xy)+xy]/[2·(-5xy)-xy]
=(-14xy)/(-11xy)
=14/11