X的平方减Y的平方加6X加9分之（X的平方加Y的平方减9）的完全平方减4乘X的平方乘Y的平方 约分是多少

[(x²+y²-9)²-4x²y²]/(x²+6x+9-y²)
=(x²+2xy+y²-9)(x²-2xy+y²-9)/[(x+3)²-y²]
=(x+y+3)(x+y-3)(x-y+3)(x-y-3)/(x+y+3)(x-y+3)
=(x+y-3)(x-y-3)