x²＋3xy＋2y²＋2x＋4y
=（x+y）（x+2y）+2(x+2y)
=(x+y+2)(x+2y)
是-3xy吧
x²－3xy－10y²＋x＋9y－2
=(x+2y)(x-5y)+2x+4y-x+5y-2
=(x+2y)(x-5y)+2(x+2y)-(x-5y+2)
=(x+2y)(x-5y+2)-(x-5y+2)
=(x+2y-1)(x-5y+2)
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