x（2次方）-1/x（2次方）-x-2除以x/2x-4
=（x-1)(x+1)/(x-2)(x+1)÷x/2(x-2)
=(x-1)/(x-2)*2(x-2)/x
=2(x-1)/x
=2-2/x
=2-2/(1/2)
=2-4
=-2