1、2x²(y+2)-3y²(x-3)-12xy =2x²y+4x²-3xy²+9y²-12xy = 2、x²-4xy+4y²-6x+12y+8 =(x-2y)²-6(x-2y)+8 =(x-2y-2)(x-2y-4) 3、x²-(2a+1)x-3a(a-1) =(x-3a)(x+a-1)
