9x²+6x+2y-y²如何因式分解?

9x²+6x+2y-y²如何因式分解?

9x²+6x+2y-y²
=(9x²-y²)+(6x+2y)
=(3x+y)(3x-y)+2(3x+y)
=(3x+y)(3x-y+2)
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