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左(2)
9b-9-3ab+a²
=9b-3ab-(9-a²)
=3b(3-a)-(3+a)(3-a)
=(3-a)(-3-a+3b)
=(3-a)(-a+3b-3)
右(1)
(与式)=x²+3xy+2x+2y²+5y-3
=x²+(3y+2)x+(y+3)(2y-1)
=(x+y+3)(x+2y-1)
(2)
(与式)=3x²-xy+6x-2y²-y+3
=3x²+(-y+6)x-(2y²+y-3)
=3x²+(-y+6)x-(2y+3)(y-1)
=(3x+2y+3){x-(y-1)}
=(3x+2y+3)(x-y+1)