（x－2分之x－x＋2分之x）÷2-x分之4x
=[(x/(x-2)-x/(x+2)]÷4x/(2-x)
=[(x²+2x-x²+2x)/(x-2)(x+2)]*(2-x)/4x
=4x/(x-2)(x+2)*(2x-)/4x
=-1/(x+2)