计算(x-y+4xyx-y)(x+y-4xyx+y)的正确结果是（）A.y2-x2B.x2-y2C.(x-y)2x2-y2（x≠y）D.x2-y2x2+y2\；

Question

计算(x-y+(4xy)/(x-y))(x+y-(4xy)/(x+y))的正确结果是（　　）
A. y²-x²
B. x²-y²
C. ((x-y)2)/(x2-y2)（x≠y）
D. (x2-y2)/(x2+y2)\；

Answer 1

(x-y+(4xy)/(x-y))(x+y-(4xy)/(x+y))
=((x-y)2+4xy)/(x-y)•((x+y)2-4xy)/(x+y)
=((x+y)2)/(x-y)•((x-y)2)/(x+y)
=（x+y）（x-y）=x²-y²，故选B．