分解因式 1.x²－xy－2y²－x－y 2.a的五次方＋a＋1 3.x²－3xy

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、...