一:[(2/3x)-(2/x+y)(x+y/3x-x-y)]÷(x-y/x)=[(2/3x)-2/(2x-y)]÷(x-y/x)=2/(3(x-y))-2x/(3(2x-y)(x-y))=(2(2x-y)-2x*3)/(3(2x-y)(x-y))=(-2(x+y))/(3(2x-y)(x-y))=(-2x-2y)/(6x^2-9xy+3y^2)二:[1/(a+b)
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