约分：x²+y²-9-2xy/x²-y²+6x+9

约分：x²+y²-9-2xy/x²-y²+6x+9
约分：x²+y²-9-2xy/x²-y²+6x+9

约分：x²+y²-9-2xy/x²-y²+6x+9
原式=[(x^2-2xy+y^2)-3^2]/[(x^2+6x+9)-y^2]
=[(x-y)^2-3^2]/[(x+3)^2-y^2]
=[(x-y+3)(x-y-3)]/[(x+3+y)(x+3-y)]
=(x-y-3)/(x+y+3)