(a-1)(a^4+1)(a^2+1)(a+1)=(a-1)(a+1)(a^2+1)(a^4+1)=(a^2-1)(a^2+1)(a^4+1)=(a^4-1)(a^4+1)=a^8-1
(a-1)(a^4+1)(a^2+1)(a+1)=[(a-1)(a+1)](a^2+1)(a^4+1)=[(a^2-1)(a^2+1)](a^4+1)=(a^4-1)(a^4+1)=a^8-1若有不懂课追问若有帮助望采纳!