1、(x²-4x+7)(x²-4x-2)+20
把x²-4x看做一个整体,则
(x²-4x+7)(x²-4x-2)+20
=(x²-4x)²+5(x²-4x)-14+20
=(x²-4x)²+5(x²-4x)+6
=(x²-4x+2)(x²-4x+3)
=(x²-4x+2)(x-1)(x-3)
2、x²+2xy-8y²-6x+18y-7
x²+2xy-8y²-6x+18y-7
＝(x-2y)(x+4y)-6x+18y-7
=(x-2y+1)(x+4y-7)
3、2x²-3xy-2y²+5x+5y-3
2x²-3xy-2y²+5x+5y-3
＝(2x+y)(x-2y)+5x+5y-3
=(2x+y-1)(x-2y+3)
4、(x²-3x+2)(x²-7x+12)+1
(x²-3x+2)(x²-7x+12)+1
=(x-1)(x-2)(x-3)(x-4)+1
=(x²-5x+4)(x²-5x+6)+1
=(x²-5x)²+10(x²-5x)+24+1
=(x²-5x+5)²