条件里括号展开,因为y不为0,所以条件可得:2x-y=2,
(4x/4x²-y²)-(1/2x+y)应该是4x/(4x²-y²)-1/(2x+y)=(4x-2x+y)/((2x+y)*(2x-y))=1/(2x-y)=1/2