1.x2－xy－2y2－x－y=x2－y2-y2－（x+y)-xy
=(x+y)(x-y）-(x+y)-xy-y2
=(x+y)(x-y-1)-y(x+y)
=(x+y)(x-2y-1)
2、a^5+a+1 =a^5+a^4+a^3+a^2-a^4-a^3-a^2+a+1
=a^3(a^2+a+1)-a^2(a^2+a+1)+a^2+a+1
=(a^2+a+1)(a^3-a^2+1)
3、x2－3xy=x(x-3y)
1.x²－xy－2y²－x－y=（x²－y²）-（xy+y²）-（x+y）=（x+y）（x－y）－y(x+y)）-（x+y)
=(x+y)(x-y-y-1)
=(x+y)(x-2y-1)
a的五次方＋a＋1
=
3.x²－3xy
=x(x-3y)
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