(x²+xy-2y²/x²-2xy+y²)-(1-xy²)(1+xy²)-x²÷1/y^4
=【（x+2y)(x-y)/(x-y)² 】-（1-x² y^4)-x² y^4
=(x+2y)/(x-y)-1+x² y^4-x² y^4
=(x+2y)/(x-y)-1
=【(x+2y)-（x-y)】/(x-y)
=3y/(x-y)
你只告诉了x,没告诉y,自己在对照题目,将x.y带入求出就行