(a²+a+1)(a²-6a+1)+12a² 对不起 =

(a^2+a+1)(a^2-6a+1)+12a^2
=[(a^2+1)+a][(a^2+1)-6a]+12a^2
=(a^2+1)^2-5a(a^2+1)-6a^2+12a^2
=(a^2+1)^2-5a(a^2+1)+6a^2
=(a^2+1-2a)(a^2+1-3a)
=(a-1)^2(a^2-3a+1)