a^3+a^2-a-1=a^3-a+a^2-1=a(a²-1)+a^2-1=(a+1)(a²-1)=(a+1)²(a-1)
a^3+a^2-a-1=a^2（a+1）-（a+1）=（a^2-1)(a+1)=(a+1)^2(a-1)
(a^3+a^2)-(a+1)=a^2(a+1)-(a+1)=(a+1)(a^2-1)=(a+1)^2(a-1)
