{2/3x-2/(x+y)[(x+y)/3x-x-y]}/【(x-y)/x】的负二次方
={2/3x-[2/(x+y)]*[(x+y)-3x(x+y)]/(3x)}*[x/(x-y)]^2
={2/3x-[2/(x+y)]*[(x+y)(1-3x)/(3x)]}*[x/(x-y)]^2
={2/3x-[2(1-3x)/(3x)]}*[x/(x-y)]^2
={2(1-1+3x)/3x}*x^2/(x-y)^2
=2x^2/(x-y)^2